Well hopefully you had something in the contract that included a penalty for backing out of the contract. If you did not, or if the contract specified that you would give a full refund on cancellation, then you are pretty much screwed. Either way, if you ask for the 5%, you are going to have a really angry customer. If you have it in writing, at least you will have the contractual authority to do it though. If you do not, you might just have to eat the cost and try to recover some of the price of the material.
I agree with Christian Brown. If there is a clause in the contract governing the cancellation or early termination of the contract, then you are okay. If not (put one in for future cases), them you may own the customer a full refund.
this is why your mom and dad should have the customer sign a contract with your mom and dad before anything is done. if you don t do it this way then things like this will happen, you might want to tell your parents to seek legal counsel to solve this problem. I know of a company that will help you in this situation. i can give you the details but not here. I don;t want to be accused of violating yahoo s answer policies./ but you can connect to me at jim_tru@yahoo.com this 37 yr old company is amazing and has solved alot of problems like yours./ but it is up to you