In my experience, it doesn't matter where the fabric came from.
I've had inexpensive fabric behave nicely and badly, I've had LQS (expensive) fabric behave nicely and badly.
I do sort the fabrics into similar colors before dunking them - Rule of thumb - if it bleeds, it won't hurt the other pieces
For example, I have five blues in my soaking water - and the water is turning blue - then I check each piece to see which one has the bad manners. After I find out which one is spilling color, I will rinse it until the water is barely colored. Usually after two or three rinses, it's clear enough.
Occasionally, a piece just wont' stop - and my personal feeling is that it doesn't deserve to be in one of my pieces. (I will try to return it or discard it - if I do keep it, I LABEL IT PROMINENTLY and put it in a ziploc bag.