How about a real life example?
Two years ago (when RVs were selling and the prices were higher than today) we purchased a 1994 Damon Intruder from a small, independent dealer. It's 35 ft. long on a Ford chassis with the 460 engine and E4OD transmission. It had 19,000 miles, no slides but a floorplan we really like with a forward facing couch in the front living room.
It was obvious someone had lived in it for an extended period of time, but the interior was in very good condition with no smells, good upholstery and new carpeting throughout.
Mechanically it was in good shape, but needed some maintenance.
When I checked the tires, the two front tires looked new and were, in fact less than a year old. However, both rear duals were desperately in need of replacement. The outer tires looked OK, but were 8 years old. Tires deteriorate with age and these were well beyond my comfort zone. I crawled under the rig and found both inside tires were the originals from 1994! Apparently that's a fairly common practice with used rig dealers - put the best looking tires on the outside of a pair of duals and assume the buyer won't notice older tires on the inside.
I kept the two front tires and replaced the four in the rear.
If I plan to keep a vehicle for a while and don't know it's history, I believe in fixing everything that looks marginal when a repair job is undertaken, instead of doing part of the job the first time and then having to do more at a later date. For example, this rig has 4 wheel disk brakes and when I drove it off the lot, one of the wheel cylinders wouldn't release, causing that brake to drag. Instead of just fixing that problem I had the shop rebuild the entire braking system with new rotors, pads, wheel cylinders and hoses. I also had them replace the master brake cylinder, as that was a fairly inexpensive addition to the job and ensured the entire braking system was up to snuff.
The engine got a tune-up with new spark plugs, ignition cap, rotor and wires, an oil change and replacement of all filters. I also replaced the thermostat, drained and refilled the coolant and flushed and refilled the transmission fluid. The rear axle got an oil change.
The dealer had replaced the starting battery, but both house batteries were toast. I also replaced the Magnetek 6300 converter with an Intellitec and Charge Wizard.
Two years later, the only problems we have had is an oven thermostat that doesn't work and serpentine belt that slips when the engine is started and the alternator is putting out maximum current. That's the one thing I didn't replace because it's hard to get to.
The original purchase price was $19k. The grand total, including all the work done to date, has been just shy of $26k.