One customer sent the following email, as a reply to receiving their invoice:

James, you are a Legend,
I have my Computer back to a normal working system now and it is working fantastically thanks to you; from the moment you walked into my house I was impressed with you politeness and calmness.
Your service, timeliness, and expert knowledge kept me calm as I watched you do your work with ease – if only I could fix things that easily.
You did an expert job on a short notice phone call and that was greatly appreciated – I will be keeping your card and giving them to people I know who have problems with their Computers.
Once again thank you.