Fabrics can and do shrink differently... even ones by the same maker, from the same collection. I would have *thought* that those at least would all behave the same, but I've learned differently.
As to eBay... I've looked at those listings, where people are selling charms or squares, all pre-washed... and I've wondered, how on EARTH do they have the time to do all that work, and sell the squares for so little? They're probably not even making minimum wage for all their efforts. Gee.