Just to clarify for you.
I don't always enforce the charging the customer for every trip rule. If the customer spent a lot of money with me and something I sold did have a problem 20 days (or even 40 days) afterwards, I would most likely take care of them. But you always send an invoice with how much it was and then zero out the balance for them. This shows the customer that your time is worth money.

It also always you however to give that invoice to that a-hole that beat you up on price in the beginning and made the job difficult. That $ per hour keeps adding up :)