Sightly off topic - I have recently had one of my big clients (optician), who has a machine upstairs, where they do all the grinding of the lenses etc. Anyhow this machine was on the floor, right next to the 'white dust' collector. This machine had a bag over the case. Complaint was that the machine wouldn't boot.
Anyhow, I get there, remove the bag, open the case up, and WOAH!. If there was 1mm of dust in there, there was 4-5mm dust build up!.
All of this grinding minute glass particles, were being sucked in from the intake fan at the front of the case. This 'dust' was everywhere. I brought it back to the workshop to clean everything out. In the end it ended up being a complete strip down (clean) and rebuild, to remove all traces off this dust. Everything was clogged up to high heaven. You would of thought that everything inside this case was white!. I'm surprised it only took out the psu.
After replacing the PSU, adding a couple of extra outtake fans, and telling my client to move this machine, either to another room (which is preferable), or somehow adding another form of dust extraction to the grinding machine, the pc is working.
I felt guilty charging my client for the strip down, and rebuild. But in the end, it all took time.
As for adding this as an additional service. I agree with the majority, it should be included in the tune up, as a free service.