They know the tenant base, median rents of different areas, how much to increase rent each year, ranges of repair costs (ex: tenant calls and says AC isn't working, no hot water, faucet is leaking, the HVAC system goes out).

- maintenance and repairs (50/month?)

Quote from @Justin Brin:  I forgot to mention that the arbitrage renter is a very experience host with good reviews for many years and with a team in place.So if that arbitrager would pay me 25% over what I make with it as a STR, covers all repairs and maintenance, then maybe. 

We always tested people out on small projects first such as doing a gut of a bathroom, 2 day repair jobs, etc. 

I will definitely ask what we can repair, replace and/ or improve as I usually do.

Bought an auto repair shop for 30% of value because of environmental problem.  

If you feel you need to do an inspection to know around how much cost it will take to rehab, then I would grab a contractor friend for a rough est, and tell your buyer the APPROX repairs needed.

If a landlord needs to enter a property for an inspection or repair, a two-day notice is required.

Regarding used mobile homes, you'd have to inspect them to see what issues and/or repairs are needed.

You should be approving repairs of that expense every time.