I think most online stores have a no return policy on cut fabric. However, if there is a defect, they will certainly help you with a return. If there is an error on the part of the store, they will usually make it right without any additional charges to you (paying postage for whatever is necessary). If it does not match what you were trying to match or it does not suit your needs, if you must return, you would be responsible for shipping. However, it is very difficult for most online stores to help you with something that does not match. If they took returns on all fabrics, then how would they sell the return? Not as easy as you may think!
If you are having a problem with a particular shop, I would certainly correspond with the owner by email to see if you can work out an arrangement which is comfortable for you both. And as for patterns and books, never returnable due to the fact that many purchase, copy them and return, which is a copyright no-no.
Does that help?