I had a call a few months ago which went something like this:
"Hello"
"Do you mend computers?" (big voice, possible senior military and retired)
"Yes, what can I do to help?"
"Just moved here from the south, plugged it all in and now the damn thing won't work"
"Not a problem (thinks - money for old rope, this one). Where are you?"
"In Leicester" (Gives me the address).
"OK - I will be in Leicester this afternoon so I will call in at about 3 if that is OK?"
"Fifteen hundred hours - right, I will be here. Cheerio."
I turn up almost on time and am ushered into a nice sort of study room in a brand new house and I have a look at the desktop PC he has set up. I turn round and walk out of the room and to the front door without saying anything.
"Oi - where are you going?"
"Back in a moment" says I, and goes to the car to fetch a kettle cable.
Watched by the Colonel, I connect the power lead to the PC, check the rest of the cables are where they should be and turn it on - and it all works just fine.
"Well that was pretty silly of me" he says, "How much do I owe you?"
"Nothing" I say, "I was almost next door and it was only a power cable and I have buckets of them".
"Thank you very very much" says the Colonel as he ushers me off the premises, "Are you sure I don't owe you anything?"
"Not at all" I say, kicking myself.
In the event it was the right thing to do as a few weeks ago the Colonel phoned and orderd a new high spec system, a decent multifunction printer and asked for help setting up his wireless router.
Sometimes these things take time to come home to roost!

I'm sure he appreciated not being laughed at and being treated with respect too. You could also wind up with a referral or two later.

Thats true - in fact I get more new clients by recommendation than from advertising.

Yes, word of mouth is the best. My brother is a contractor and he has such a great reputationj for honesty and superior work he hasn't had to advertise for years. What goes around comes around.