How much wear and tear also is related to what chassis is under the Class C ... E350 or E450.
Wear and tear of course afffects other things other than just the engine and transmission. The E450 would have had an easier time at towing than an E350: The E450 has bigger brakes, a lower range rear differential ratio, less transmission clutch slippage due to the lower range rear differential ratio, a larger diameter driveshaft, and thicker metal used for it's frame.
Even if the Class C is on an E450 chassis, wear and tear also has to do with what size the Class C is due to raw weight. A large Class C that was used for towing would of course have placed more stress on all chassis components than a large Class C that was not used for towing.
If the Class C you're considering was around 27 feet, or less, and on an E450 chassis and had been towing only a small toad ... then probably it should be OK from an additional stress perspective.
