The person that got scammed provided the necessary proof to GOG and shared some of the details with me.

Well, sad they got scammed, but good on the banning of scamming types!

Very sad indeed.
Even sadder that he still succeeds at it; I'm pretty sure this is not the last we've heard of him - unfortunately :(

So what did Wakalo do to scam people?

Lots of things
http://www.gog.com/forum/general/known_scammers/post1

Were you not sleeping? sleepwalking sigil speakchimp.

Until my inbox flooded with PM's (perhaps inboxes as it was variosu channels) i had intended to. Now... IM StILL BLOODY AWAKE! O_o,~

Yikes. Like SimonG said in one of those threads, what a prick.

I liked this idea that someone had: But how does one check the validity of a code without redeeming it to their own account? I didn't think that was possible.

maybe if you read more of the thread you will see...

Yeah, sorry *hangs head* just doing so now and learning more and more...

Shit happens mate, or in this case "inboxes happens".

sadly there is no way of checking a code besides activating it.
even if one already owns said game it will just tell you if the code is valid and not if it was used already.

Well... scammers & all... do keep in mind they're just games. If it's not fun anymore it might be time for a different hobby.

Have:
outlast (steam)
interested in Dreamfall: the longest journey(gog)
please pm

also have
desura:

paradigm shift
decalc
defenders of the last colony
zombusters
Zafehouse: diaries
Zombies ruined my day
fairy bloom freesia
radical roach
millenium 2
oknytt
inverto
diehard dungeon
end my world
manor of the damned

Steam:
A walk in the dark
greed: black border
slam bolt scrappers
obulis
project aftermath
hydrophobia prophecy

iron grip marauders $10 content coupon
big head bash content pack

Good trades with:
momo1991,cj13810, Giltonnam, Heretic777, Tarnicus, triock, Azrael360, MoonGoddess, 09167, roygbiv309, pandaliang, undeadcow, alexkoti, roelibex

It appears that WWTDead got a bit annoyed with me - see attached screenshot.
He PMed me to:
1. Whine that my post deprived him from getting more loot via scamming - ironic he uses the term "trade" given that he never gives anything in return.
2. Brag what a successful thief he is here and on other places - he actually mentions real money he's stolen.
3. Mock us for not giving him what he wants fast enough - I guess he's after more expensive games than those offered for trade.
4. Warn us that he'll be back for the Christmas season - I assume that's because he expects more new users to discover both GOG and the Classifieds thread. Still, I wouldn't put any trust in his comment that the next couple of weeks are any safer.

Notice how he PMed me after he was banned, which leads me to assume that forum and PM privileges are separate, i.e. he may be banned from the forum but he can still freely contact any member through PM.

So, take this post as a warning - in addition to any open offers in this thread, be extra careful with any PMs you might receive in relation to trading.