Valve has updated their Scam FAQ according to PCGamesN, saying they will no longer be returning items to scam victims, saying "All trade scams can be avoided." To that end, they offer an extensive guide on scam avoidance. Here's the explanation for why items will not be returned:

Our community assigns an item a value that is at least partially determined by that item's scarcity. If more copies of the item are added to the economy through inventory rollbacks, the value of every other instance of that item would be reduced.

We sympathize with people who fall victim to scams, but we provide enough information on our website and within our trading system to help users make good trading decisions. All trade scams can be avoided.