The simple solution is to ask for all mats up front, including the crystals. If they whine, simply say, "I'd love to help you out, but I ran out of crystals." And of course if you're wishing to be compensated for it, ask it up front.

This reminds me of my deployment to Egypt. We were warned that if we purchased a service from a vendor, to get everything paid up front. See.. what they'll do is offer to take your picture on a camel. Its a dollar to get on the camel. Its ten dollars to get off. Five dollars to get your picture taken. And in the case of one guy in the unit, eighty dollars to get his camera back. In the western world, thats extortion. In that part of the world, business as usual.

Point being, make sure you are up front about the cost of the craft. Its borderline extortion to make someone an item, dangle it in front of them and ask for payment. Especially if they gave any mats for it.