Yeah, same as.

To improve your chances of getting that extra mile service I also have a few tips I learned from a friend who is a mobile windscreen fitter which I'm sure are equally valid here:

1. Be pleasant. Don't get in a huff if they are late. It will almost NEVER help to get ratty with the installer, it's probably not THEIR fault anyhow.

2. Be curteous and offer them a cup of tea/coffee (cake/biscuits/sandwiches are a real bonus).

3. Have a pocket full of coins. When you talk with the fitter(s) jingle the coins (like you are keen to spend them). This (and the tea) usually labels you as a tipper in their eyes.

Usually you don't need to give large tips, a few quid is generally sufficient.

If this still doesn't get you what you want then, as a last resort, pull some notes from your pocket and offer to pay for any out-of-spec work - it's important to mention you don't want a receipt!