I think the trick is to try to find one where everything is working on it when you buy it. Granted it is used and things fall apart as time goes on. If you get a decent deal used, in many cases, the future repairs and maintenance will still be cheaper than buying and maintaining new.
It's easier to upgrade an old rig more to your liking, because you are replacing old stuff with new stuff. If you start customizing a new rig, then you are replacing new stuff with new stuff, and not gaining much ground there.
New rigs are not maintenance free and some folks end up tethered to the dealer until they get all the warranty mess sorted out.
In my case, I opted to pay cash for a used rig with zero financing. My repairs, maintenance and upgrades have been far far cheaper than payments on a new rig. Also as things need repairing, I am able to upgrade to my liking. For instance many motorhomes come with cheap faucets and I wanted a nice retractable faucet with single hand controls. If you switch this out in a new motorhome, you are yanking out a new faucet to put in a decent one, but in my case I was tearing out a 15 year old faucet to put in a new fancy one.
On used rigs the engine schedule is typically out of whack, because the mileage isn't that high per year. You just have to use some common sense and try to locate a decent mechanic (very hard to find!) I find a pretty good shop for my engine, I went in with my list of work, which they did, but they also wrote down a punch list of suggested repairs and maintenance. I crossed off the ones I could do myself and the rest we talked about and I pretty much went with their recommendations. I had to postpone a few items (my budget needed a new infusion first) but still, I was extremely lucky. The engine has been purring along taking me places without complaint.
The biggest pitfall I see is the folks that advertise their rigs that need"minor" repairs then claim you can do them all real cheaply. If they were that cheap to repair, the owner would do them before selling it. But some RV owners are clueless about their rigs despite owning them for years. It's understandable that many do not do their own work, but some never think to get a 2nd opinion on "major" repair estimates that may not be major at all.
Some RV places create MAJOR repairs out of minor ones.
Even when you need repairs on a used rig, I have learned to shop around. Some places will only "repair" things by forcing a new replacement on you. Others are willing to repair the existing equipment. For instance when my air conditioner fan died overnight, the first 3 shops I talked to refused to repair the fan, insisting I needed a whole new AC unit because mine was old.
The 4th place, couldn't repair the fan but replaced it with a used fan very reasonably and the AC has been working fine for 2 years now. Yes, you read that right, a used fan. He was willing to rip a running fan out of an old unit he had out back that had a dead condenser. We both came out ahead on this deal.
Recently when my furnace refused to start one day,I popped the cover off the thermostat and brushed out the dust, but it still wouldn't start. I checked to make sure the propane tank was working (everything else lit up fine.) I took off the furnace cover and stared at it a good long time... Well, um, that was the extent of my repair knowledge on furnaces!
Many dealers and repairmen would have you believe that equipment can be fine one day and completely dead the next requiring a brand new replacement. While this might be true in a few cases, sometimes a wire is loose or something needs cleaning or it needs a minor part.
One shop wanted $299 for what they called annual furnace maintenance and I would have to leave my rig with them for several days. Apparently they don't like to work with fulltimers and can't schedule a repair to start at a specific time. "Just leave it here a few days and we'll get around to it". I wasn't about to uproot my dog and I to relocate to a hotel because of their lack of organization.
The next guy I talked to, popped the cover back off the thermostat, cleaned the contacts, started the furnace and said "Well, that's fixed now! What else you want me to do?" I was so impressed, I gave him my entire punch list and he ran around fixing and diagnosing. Most things he repaired in just a few minutes, others needed a minor part he had to track down and repair later.