In the past Valve use to restore items lost to the original owner but not take the item from the scammer itself. This changed now after Valve amended their TOS and it's "Scam FAQ". In this new FAQ update, Valve explains that if they restore items and leave another copy of the item out there, that the value of that item decreases.
The way that item values are determined are by the community assigning a value. This value is partially determined by the limited or non-limited amount of that item. If Valve does inventory rollbacks, the value of that item is diminished.
They also explained that while they are sorry people are getting scammed, they provide enough information in the "Trading FAQ" to help users make good choices on who they deal with and hope the community makes good choices. They also commented that "All scams can be avoided."
This new TOS was most likely adopted because of inventory rollbacks consuming a lot of time and money for the customer service department of the company. They have already been dealing with refunds (in certain circumstances) for games purchased online.
Watch out for this new update and remember to be careful with who you deal with. Also if you want 100% reliability and peace of mind, just purchase the game from Steam itself.
I'd also like to thank Sparfire for the idea.