I've NEVER read in these forums of anyone rejecting a used or new RV at purchase time due to a built-in generator being too loud. They may definitely want a built-in generator and would pass on an RV without one ... but have the dealer or current owner start the generator and then the prospective buyer reject the purchase if they didn't like what they heard ... doesn't seem to be happening.
I sure read a lot of owner complaints in these forums of too-loud, and/or too-smelly, and/or too-much-vibration built-in generators in their rigs. We can stop this over time by not buying RVs anymore with poor generator installations. For the price we pay for those built-ins in order to gain self-containment .... we deserve better and the only way to get it is to vote with our feet and wallets.