I used to charge £40p/h lol, if I less than 15 mins, they would get the callout for free. This rarely happened, but when it did. The cust was more than greatful and bobs your uncle, 10 calls the day after from that cust's relatives/friends and stuff hoping they can get a quick free fix.
The catch though... Dead simple, honesty!
I would sit there for 15 mins, work out the exact issue, let the cust know, roughly how many hours it would take and go from there. If they said 'no thanks' I would simply hand them a card with my number on, let them know what the issue is without a description of fixing it and walk away. Never, ever did I not get a call back.
"Roger, the computer is still not working"
"IT guy wanted £40 to fix it!"
"It cost £600... pc world want £120"
"Fine you old hag... *Ring* Hey, it's Roger, mind rebooking?"
Kaching.
ags
So true, good way of hooking them as well as getting good word of mouth around. Sneaky bugger..