In general:
If I find a game-breaking mechanic that I can use, I'd inform the mod and see if he thinks it wise to change the rules in this case (ideally, with a concretenew rule/restriction like changing my ability to n-shot or preventing me from using it on a particular player.)

In the specific example you gave, that's just terrible. If it was me I'd immediately inform the mod before the game started and just ask him to change the setup. Unless by some miracle he can find a way to change the rules to nullify the game-breaking advantage, but I can't see this possible. Note that: "new rule: you can't tell others who the mafia are" is not a concrete rule and extremely hard to implement. Where do I draw the line? As a player I am expected to make reads, so what reads can I do against them? What I find them real scummy? But how can I tell if I do find them scummy or am just saying so because I know they are.

As town I'd feel not happy either way. I won, but did I really win if my opponent had by himself to put aside a winning strategy?

Also note that putting restrictions on yourself, in general, is a bad idea because unlike the mod you don't know the full setup. You might be thinking you're being a good sport nullifying an unfair advantage that you have, but in reality the other faction might already be somehow compensated for it, and you're in effect under-powering your own team.
Pretty much, yes.
Scenario:

Tragic town lover: you win if You and Mafia lover survive OR if town wins normally (all mafia are eliminated - in which case your partner loses)

Tragic mafia lover: you win if you and Town lover survive OR if mafia wins normally (they obtain lynch control - in which case your partner loses).

(Note that the common win condition means that both regular town and regular mafia lose).

You are mafia lover, and you agree to go for the co-op win only. Yet as soon as the situation becomes TTTLL, he decides it's too much trouble to go for it, and just outs you and wins. You feel betrayed and hold it against him.

But if you were one of the T, don't you think that there was an implied agreement between all Ts (including the lover) to go for the Town win? Would you feel betrayed that L(t) went for the co-op win condition causing you to lose? Didn't your implied agreement essentially mean he betrayed you?

EDIT:
OK, I read your post and in the latter case you'd hold it against the mod for being bastardish. But the lover did have the same condition as you in the above scenario. And he decided to go for the other one.

Case 1: I'm the mafia lover, and my town lover and I agree that we're going to play for the co-op win. I'll trust him, and I'll play for the co-op win. If he decides to betray me late game (especially without notice), then I'd call that a betrayal of trust. Tit-For-Tat comparison: we agreed, so I'll play Tit expecting him to do the same. if I later have a chance to Tat for his Tat, then I may go for it.

Circumstances apply: if we realize that we're out of luck for our joint win, but he could possibly still meet his alternate win, then I may be willing to eat the loss to let at least him go for victory. Ideally, this should be discussed and agreed upon before hand.

Case 2: I'm town, and there is a Tragic Lover pair (don't know who) in the setup. I don't expect any given other player (including the Town Tragic Lover) to be playing for my win condition, though I do expect townies to generally be playing for town. If the Town Lover chooses to ditch the town, then "Them's the breaks"; there was no agreement to play for town even though an alternative victory was available to them.

Case 3: Mod-confirms that a given player is a Town Tragic Lover ("Why would the mod do this?" is left as an exercise for the reader). If the TTL agrees to play for town, then I expect them to live up to that, or some Tit-For-Tat may show up later as encouragement not to betray again. I do NOT expect them to make the agreement in the first place, and if they don't agree to play for town then I don't expect them to necessarily play for Town.

Of course, if they don't agree to play for town, then I'll naturally consider them a potential enemy. ;)

Case 4: Mod-confirms that a given player is a Town Tragic Lover, when the player actually needs Town to lose in order for the player to win. I'd blame the mod/setup.

If the game was stated at the outset to have bastard mod elements, then I'm fine with it. Everyone knows that such a game may have some unfair/unbalanced aspects. This can allow for some amusing twists that wouldn't be appropriate for a "normal" game. See Bler's game 38 for a good example of this.

Clarification:

I expect each player to play to their win condition(s).

If a player makes a gentlemen's agreement NOT to play toward some condition, then I'll generally expect them to honor the agreement. A TTL has two win conditions; if they (freely) agree to limit themself to playing for a single option, then I generally expect them to do so. If they don't make such an agreement, then they're free to play toward whichever win conditions they think they can achieve. Agreements reached under duress are subject to suspicion.

Individual circumstances can, of course, vary the general rule.

OK. I can understand where you're coming from. Though personally I feel a bit differently.

I play for my win condition, and that's it. I expect you and all players to try your best to play for a win and that's it. So if I'm ever lovers with you (I mean in-game lovers!) then "I play for my win" is all you're going to hear from me; no gentlemanly agreements of any kind.

This applies to all setups with variable winning conditions. e.g. If my best chance of winning in a cult game is to get recruited and have my win condition changed, you can be sure I'll be trying my darned best to get recruited.

If I win and learn my opponent could have easily won using an in-game mechanic but chose to be a "good sport" and not use it, I'd feel my win a bit undeserved. And be a bit pissed at my opponent. But more pissed at the mod for a setup that puts me in a no-win situation (I either lose; or get an "undeserved" win so it's a lose-lose).

Conversely I'd never hold it against my opponent for using an in-game "cheesy" tactic to beat me. If anyone, the mod is to blame for making a setup which allows such cheesy play.

But all that applies only to in-game "lying". A gentlemanly agreement made outside the game is to be respected, period. If my opponent has a real life situation that would make him unavailable and I make a gentlemanly promise that I won't hammer while he's gone; then I'd never hammer while he's gone, my win condition be damned. (And any player lying in such a way would deserve more than tit-for-tat in my book; do it purposefully multiple times and you get into my "won't play with" list).

Also clarification:
When I say I'd blame the mod for allowing a cheesy way to win, I mean a broken setup, not an unbalanced one.

An unbalanced setup might be 12 T vs 2 M. T have bigger chance of winning, but a good mafia player might still find it a fun challenge to try and win regardless.
A broken setup might be one with follow-the-cop. It might appear balanced, but there is a game-breaking tactic.

I'd never blame a mod for an unbalanced setup, even if it puts me on a "weaker" team. In fact, like SPF said I'll take a fun unbalanced setup any day.
I would "blame" a mod for a broken setup even if it puts me on the "winning" team.

(And I sincerely hope my game was the former; maybe swingy and unbalanced but at least fun to play).

Just seen in the observer thread that trent had a plan.

also that scene lied about being in a meeting at work when he wrote his claim: that's hilarious.

Sorry again both of you. I was genuinely excited to be on a team with you, my first reaction was "yay this team's gonna be unbeatable"... then I read the restof my role...

Hopefully we'll get another chance to work for the greater evil

I read that and wasn't going to comment, but I think it's actually problematic.

When people make claims about RL we generally honor them as true because calling people out for RL is shitty and generally sucks to be on the receiving end of.

Lying about RL as an in-game strat...is a very dangerous door to open.

I actually agree here. Didn't want to comment while game was still in progress, but I'd ask people not to do it. Lying about RL interfering with your posting is close to breaking rule 3.

eh, maybe. In this situation it was more funny than it was damaging. Especially the way he confessed.

but alright, from now on I shall tell only 'game lies'

Ah yeah, I agree that lying about RL problems is an "out of game" lie and not really excusable by being mafia. I had a similar problem in a game a long time ago where a player (who turned out to be mafia) lied about the mod making a mistake. They got caught in a lie and when pressed they said something along the lines of "Oh, the mod has just PM'd me and told me there was a mistake in the previous PM!".

Couple of questions from a noob.

Why wasn't there more suspicion about the brothers surviving the last night?

HSL, why didn't you try to save mchack since you seemed to believe him?

Trent, did you ever feel there was something more going on with Joe before and after he claimed?

I wasn't in the game, but a big issue is it's classic WIFOM.

If they were town surely scum would kill them, therefore scum don't kill them to make them look suspicious so that town will mislynch them.

There's also the issue that killing 1 in some cases impacts MAJ whereas in some cases it doesn't, and that mafia may also perceive other players as being more immediately dangerous - whether because of how they would vote, or a perceived to keep role-hunting (twins didn't claim doctor, after all), etc.

As others have noted, the night before they had the excuse of killing Flub (only confirmed town), so if the twins were town, mafia really only fired elsewhere definitively the one time.

So there's a lot of reasons. If they'd had to claim D1, then yeah, it would've gotten more suspicious over time, but it was really only the one night where scum chose a questionable target, and strategically that's just not a big variance given wifom and other possible explanations.

Question for you: why haven't you signed up for the new game yet?

And in case muddysneakers hasn't googled that abbreviation yet: Commonly Used Abbreviations