Maybe DC will chime in on whether this is useful or not but I do this.
Take the material over by the windows and hold up to the light - how well can you see through it? Pull it by opposite corners and "the middle" and see how much give there is. Look at the back to see what the 'construction' or weave that is holding the front pattern together looks like. Feel for thickness, and sturdiness. Look to see if the threading creating any pattern would be subject to creating pulls.
My thinking, which may not be of much use, is that the more a fabric stretches, the more light you can see through it, the looser the backing weave means more give. Every time you sit down something is rubbing up against some other thread as it gives.
Now I suppose its true that if you had a really tightly constructed fabric made of cheap threads it does'nt matter as they will just eventually snap whether they give and rub together or not. But hopefully thats a minority.