Water damage is sometimes easy to see and sometimes difficult. Water stains on ceiling, wall coverings, or flooring is one obvious. Soft spots in the floor (under the floor covering) is another clue. Evidence of re-caulking on roof or side seams is not unusual, but very much of its suggests that looking for further clues inside might be wise.
I too consider that replacing a genset is highly unusual, both because of the cost (multi-thousand dollars) and the relatively young age. That raises a flag in my mind, either false advertising or unusual wear & tear. Replacement floor covering in an '08 also suggests more than typical wear & tear, but so does the 97k miles.
Few sellers put a lot of money into repairs before selling, so I would ask more questions about when and what was actually done.
All signs are that this rig is thoroughly used. Presumably the price is attractive, but maybe spending a bit more for a lighter use rig would be a better choice? In any case, the signs are that you should inspect the rig carefully and proceed cautiously. Get a professional inspector if you cannot judge for yourself.