Same thing happened to me. I swapped blocks of good quality fabric. My blocks were squared to the correct size. I used the colors required for the block, light/med/dark. The blocks I received were not usable. Some blocks weren't even the right size, too small. The fabrics were so thin I could see through them. Some blocks didn't even have the dark/light 4 patch right. Out of 14 blocks there were only a few I could use.
I ended up making most of the blocks myself for the quilt top. That was my first and last swap. Maybe you should mention the poor quality of the blocks to whomever hosted the swap.(?)
Definitly a lesson learned.