My reply is no i do servers
And if pressed explain its like getting a truck mechanic to have a look at your lawn mower,
if they persist further, i say all right at an hourly rate of half my existing tab, that usually is enough to make people stop once they realise that it wont be a freebie.
That said it very much depends who is asking, as im quite prepared to do labour swaps with other trades, as they instantly get where your coming from if you flip the question back at them as they know "could you just" really means "could you do a job you would usually charge for because we are stood at a bar together and i buy you a pint (actaully worth 30mins of work at min wage tops) you will do it for free" you can get good results, i.e. got my boiler serviced minus the plumbers labour charge in exchange for fixing his lads PC, and my cam belt swapped out for the cost of a new belt, for fixing a snap on branded diagnostics PC, so yeah when it benefits me i will fix your computer ;-)