I'll give a little anecdote of my purchasing of my first motorhome - as opposed to having self-build campers previously.....
First potential purchase and one I put down a deposit on needed a fair bit of remedial work needed - and I gave the dealer a two page list of everything I wanted doing - and which he agreed to fix

Unfortunately this was in 2020 and in the midst of the Covid Lockdown, so had the twin problem of staff going off-sick/isolating and suppliers not supplying parts that were needed.
So that purchase was aborted after around a month and deposit returned (with absolutely no problem, btw).
Next potential purchase was successful. Being a private purchase, no warranties and any problems would need to be identified and remedy negotiated.
Spent maybe 3 or more hours looking at vehicle and chatting to owner. IMO, doing an "owner inspection" can be as revealing as a vehicle inspection as you get a feeling of how they used and looked after the vehicle.
Things I identified were:
Leisure batteries were old. As I intended to update all the electrics, didn't matter.
Tyres were ok tread-wise but brand-mismatched. Some people wouldn't care; I like them matching and as I wanted to switch to Michelin Cross-Climates, again didn't matter.
Only problem that I encountered post-purchase within what would have been within a dealer-warranty period and would expect fixed if bought that way was the Shurflo pump had a self-priming issue. Worked in use no problem at all, but couldn't prime if tank allowed to empty before refill. Spoke to owner to see if any suggestions on this (as not mentioned by him) and following his process, sorted out issue (more later on this))
Now talking about "owner inspection", when he delivered the motorhome to me, he spent 2-3 hours doing a handover on how to use everything, and then quizzed me on how to do various things to make sure I was listening! A sign to me of someone who was proud of what they had and wanted to make sure it would continue to be looked after.
The water pump issue I have no doubt would have been mentioned if he remembered, but his way of dealing with it was simply to not let the water run out and after over 10 years of using it this way, would have simply forgotten about. In the end, I got fed up with messing about with the priming process and decided to buy a new pump about 18 months into ownership. This fixed the issue instantly at a cost of £65.
In my ownership of over 5 years, spent a fair bit on maintenance and repairs on the vehicle, but those costs are virtually all around the Fiat Ducato base vehicle and not for the Autotrail Motorhome part.
Sure, spent a tidy sum on the Motorhome side as well, but these were 99% optional upgrades and enhancements to make it more comfortable and nicer to use (and IMO, my near-18 year old motorhome in use is now nicer to be in than just about any other motorhome I have been in, new or old).