I'm not a legal expert, but I've been told that if you somehow end up in court, the whole 'customer supplied parts come with no warranty' won't hold water. Can't remember exactly how it was explained, but in today's world, it's not worth the risk/headache. I will say though, props to you for charging 1.5X the labor rate. That's probably the only way I would consider customer supplied parts, with a clear understanding that if there is any delay related to the parts, the customer is getting charged 1.5 the labor rate for the time it ties up a stall.