This subject comes up from time to time, and I'm not aware of anyone who does this for a living. You might try talking to a tech at a dealership to see if they would do it during their off hours. Meanwhile, we have a number of checklists in our forum Library (button in the toolbar above) that might help if you decide to do it yourself.
This guy drove about 45 minutes to the MH. He was there for about 2 hours going over this thing. In it, under it, on it. Checked all appliances, gen set, more than I would of had a clue to look at. At the end of it all he stated if I was happy with the price that I should buy the unit. And I did !! He charged me $130. For me it was well worth it. Piece of mind knowing this thing checked out ok .
You can engage the services of a mobile RV tech to do this sort of thing. Some will give an ad hoc check-out, while others will only work to specific instructions, i.e. do x, y, and z. We have checklists in the RVforum library on things to look at when buying an RV. You could use those, or a subset, as the basis for hiring an RV tech for an inspection. Expect to pay by the hour, including travel time.
We bought our trailer (18' Funfinder) at a Repo auction back in Sept. When we were looking it over a couple days before hand there was an RV tech doing some winterizing to a couple other units. Gave him $50 and he did an inspection for us - checked that everything fired up, power worked, tires were good, and no signs of leaking. Was $50 well spent in our minds and helped us set what we thought was a reasonable limit for us.