What you are getting on welfare is earmarked for you and your family only. The government hands you a gift that you have stewardship over.

The thrift store is just a store that provides used things at a discount. I see no difference buying something from there, a garage sale, or used book store. Reselling the item that you bought with your own money at a profit is not an immoral act. If the store is specifically set up as a place for the needy, then sure the rich guys shouldn't go in there and look for stuff.