If you give something away to someone and they sell it, it should not affect you.

It turns out you gave them money, and not the thing you thought you were giving them. Either way, you don't have it any more and it isn't yours to decide it's future. If the person who owns the thing would like money in lieu of the thing you give them, tell them to wait for you to sell it and then you will give them the money.

Then of course once you had the money you might re-consider that position.

Garage sales suck, and we have one almost every year. Don't get excited, it is almost 100% little girls clothes.