I'll be the voice of dissent. Our class C is a previous rental. We're the second post-rental owners as a matter of fact. Ours was at a smaller dealer (who got out of the rental business), and was only in rental service for a couple of years.
We wanted the Winnebago brand and were willing to go with a previous rental so we could get the quality at a discount. I think fit and finish and "extra goodies" depends on the manufacturer and what the the renting dealer specs out for the rig. For us, we preferred that a rental would have more durable fixtures and some idiot-proofing. We've de-idiot-proofed a couple of things like the screwed down access to the water pump (a $3 piano hinge took care of that ) but left some stuff intact like the plexiglass over the lower portion of the screen door
We also made sure that the previous rental we bought didn't have a ladder - less likely that renters would have used the roof as a patio. Though Winnies have walkable fiberglass roofs, but still nobody should be up there unless they know what they're doing. We did have a ladder installed for our own easy access, though
We also have a slide, which seems to not be typical in the previous rental world. And the previous owner put awnings on both the door side and on the slide out, which I really like. Awnings can always be added, of course. Slides, no.
We were comfortable buying a rental since there were service records showing that it was maintained regularly and I'd also rather have something that got some engine and genny exercise rather than sitting idle in someone's field somewhere. The tires were replaced for us when we bought it, and it had something like 22,000 miles on it. So it was used, but not driven into the ground.
Fit and finish in our Winnie is head and shoulders beyond the Gulf Stream travel trailer we had. Real wood cabinetry with ball bearing drawer glides, much more durable upholstery, etc.
And as for people trashing them, I think some of that may be fact, but some may be myth. Look into renting - you pretty much promise your first born in exchange for any clean-up they need to do. I have to think that most families that are looking for a fun family vacation are being respectful of something they're paying hundreds/thousands to use. And I wasn't too worried about someone having done something awful to the E-450 chassis/engine since they're pretty idiot-proof themselves.
We've put almost 5,000 miles on it since we got her last spring and have had relatively little problems, except a phantom slide closure issue that we worked with Winnebago and the slide control manufacturer to resolve - it was a short in the slide control, highly unlikely that it was something a renter caused, unless they purposely broke the moisture seal on the unit
All that said, I think I'd be wary of buying from one of the high-volume places unless I really knew what I was looking for/at. But there are plenty of success stories out there as well.
Here's a good thread from the Class C forum at RV.net with actual owners of previous rentals discussing pros and cons:
http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/26035008/srt/pa/pging/1/page/1