I once did something like this at a quilt store. We had to buy the batik fabric, pay a couple bucks for the background fabric and enter the contest. I won the blocks but the fabric store owner didn’t reserve enough of the background so she substituted and the blocks didn’t work well together. Decided right then and there that I’m picky and these swaps aren’t for me. Also I once bought a lovely set of blocks sewed together on this board for $10 and when I received it, it was just horribly sewed, it wouldn’t lie flat if I steam rolled it. I stick to my own blocks for now.