I guess I have lucky, I never make a sample block. When I start a quilt I am committed to make it no matter what. I just know it will go well. Dumb luck I guess.
I always wash and dry fabrics before using and I wash and dry the finished quilt. Luckily the fabrics I buy don't bleed or not much. From reading on this board the more expensive fabrics bleed more than mid cost. Since I give most of my quilts away, I only buy fabrics I can afford. I use quilts for our bed(about6-8) from the same fabrics and they have held up very well.