Too Busy to Collect

My mechanic is still so backed up with work that he hasn't had time to draw up a bill for me. I went by this morning and after waiting for the two sets of customers ahead of me, asked him to give me a call whenever he's ready for me to come pay for the work he's done for me. I'd give him more referrals, but he's doing so well that it doesn't look to me like he could handle any more work in his existing shop.