I pretty much agree with just about everything that has been said before with one really big exception for me - I will never, ever purchase prewashed fabrics. I do not prewash and have never had a problem - use color catchers if needed. At one of my smaller guilds I belong to had a scraps sale. We ask members for any reasonable sized scraps but they must not have been washed (gives the purchaser the option if wash or no wash). We used zip bags to be stuffed with as much as possible as long as it could be closed, for a very reasonable price - think we used quart and gallon sized bags - different for the smaller one than the larger one. I have also purchased yardage from a home sale as long as the measure was noted and had not been washed,
Sandy in Mooresville, NC (still visiting in CO)