I'm sorry but if he's doing that it's because people allows him to.
You want to give the extra games from this sale? Make the rep requirement match the price requirement for the unlocks:
1 Rep for Simcity
20 Rep for Stalker CS
50 Rep for Xenonauts
Want to gift other games?
You need to have an account before "x"date
You need "x" rep
Sorry for the new users but rules need to be created (used) to prevent this kind of situation, you can't expect that every new user will be a good person that won't take advantage of you...
We definitely need something like that set in place.