I don't want shoes that are too small and I want to sell them for a bigger pair.
Why do you want bigger shoes?
Because I need a bigger shoe than this and I would rather buy and new one than getting the big one.
If the shoes you got are too small, it's fine to return them and get a bigger pair. You could get sized at the shoe store so you can get the proper fit.
Nah, I'm going to sell them on eBay.
Well even if you do sell them on eBay you need to make sure your next pair fits you well so you don't have to go through with this again.