Crafting coins can be bought and immediately uncrafted. Losing nothing. The Coin Spender and Item collector badges can be achieved with this but I didn't test enough to see if you can get Item Crafter from it.
Actually not an exploit, if people wish to use this method they will need to spend a lot of time doing so. "Exploiting" badges is not a thing as long as they are obtained how they are intended to be. (In this case, crafting items and buying items from the shop)