Personally I tend to be 10X cautious with a rented car because I never pay for full assurance coverage, because I feel it like being robbed (the same way renting a child's seat makes you feel, I paid more for the seat that for the car itself)
I used to run 'rental cars' (aka cabs) into the ground on a regular basis just because you're not making any money sitting around waiting on a wrecker. Plus, the company generally didn't fix the cars unless they were towed in, can't even count how many times I'd swap out of a car after telling them what's wrong with it and see a message the next morning about needing a passenger rescue on that car because the mechanics just sent it back out without even looking at it beyond "well, it starts and drives around the yard".
The last cab company I worked for had an unofficial policy (on 'voucher' trips which were billed to insurance companies and whatnot) that if you got the passenger in the car you'd get paid for the trip so if you have a $100+ trip on your screen and the car can somehow limp to the pickup address then this what you do without worrying about what it'll do to the car...
I didn't intentionally tear up the cars but after a while I learned what a Prius could take. No AC in the Arizona summer, straight back to the yard. Car makes a big thumping noise taking off from every stop, probably be OK for a day or two before finding a better car to swap into.
Can't imagine rideshare drivers care any more about the cars than I ever did.
Anecdotally, the folks checking over the vehicle before taking it back also do quite a poor job and miss things. A friend of mine I was helping move put a solid dent in the box of a u-haul and they didn't even notice.
Low-octane gas will cause problems in older carbureted cars, but most cars sold in the last thirty-or-so years will not have this problem.