My mechanic told me the install of the part I bought and brought to the shop should take an hour. It took 2, mostly because my part came with fittings that didn't fit my vehicle. My mechanic apologized for the delay, and didn't charge me more than the quoted hour. He could have, and I'm sure many shops would have, and I would have paid. But he wants to keep customers happy, so he doesn't worry about the small stuff.

When I was consulting and billing hourly, once the first hour was past, I never incremented to the next hour, until I gave them a full hour of work . They knew I spent many fractional hours on them for free, and that built trust and loyalty.

If you treat your clients the way you would like to be treated as a client, if you do little things for them that lets them know you are thinking about them, but do them without expectation of immediate reward you can gain loyalty, and it always costs less to keep a customer happy than to find a new one.