You're right. I don't have any concerns about assessing the quality and condition of the house systems, body, etc. and there are mechanics to evaluate the engine/drive train, etc.
My major concern is not overpaying. With all I've read about NADA, etc. determining a fair buying price for a used rig, in particular, is pretty much a crapshoot.
Thanks for the info on the buyer's agent, it looks like they don't exist.
I'll be posting another topic dealing with our needs for accommodating a wheelchair, which severely limits the number of suitable rigs (resulting in fewer opportunities for pricing comparisons and negotiations). We don't need full, ADA accessibility but we do need a minimum of 27" clear access at the entry door and in all passage ways plus reasonable (but not ADA) bed/toilet/bath access. I have a lift solution identified.
It's amazing how many rigs look like they'll work and then there's a 25" choke point somewhere. I've measured 10 to 12 30' - 33' motorhomes in the past week or so and only about 3 models will work.