Help me understands something, please

I'm just curious what kind of measures are taken to prevent people from creating private groups among friends with private giveaways in which only one friend enters and claims to have received the gift though there was no gift to be given?

I'm not sure I phrased that well enough....

Person A makes a private group and a private giveaway on steamgifts.
Person B Enters, alone, that giveaway and wins.
no game is ever exchanged
Person B marks game as received
Person A is now a contributor.

It seems this would be really difficult to keep track of =\
but....
In light of this guy and his "winnings" I fear there is serious abuse.
---> http://www.steamgifts.com/user/coldchar/won <---

If this is a wasted forum thread I'll close it