I was once dating a man who was to be a pallbearer at a funeral. We went to the men's store and I helped him find a new suit at a reasonable price. However, he refused to pay for the tailoring to get the suit fitted. He figured I could do it. I was working, plus doing distance education, plus my sewing room was not yet set up since my last move, but he failed to understand that I could not get the suit altered in time for the funeral (not to mention the fact that tailoring is not my thing anyway). He actually got verbally abusive over it. Needless to say, I am no longer in that relationship.
When a friend asked if I could crochet something for a baby in her family, she was more than willing to pay good money for it. I just didn't have the time. And personally, my crafts are for my pleasure, not for profit.
Use that backbone. You have every right to say no without guilt.