I can't think of any situation where I'd let a buyer move into a move-in ready home of mine prior to closing.If for some reason the property doesn't close, the best case is that I have to wait for them to voluntarily move out, will have to touch up the paint, clean the carpets they messed up, clean the toilets/sinks/showers, and fix the nail holes in the wall.

No squatting here.

I have afew who do final cleanupThat was usually on meI also was putting a pack of lightbulbs and four pack of toilet paper in them that I always paid for.

Figure out everything that it takes to make the place work (appliances, cabinets, flooring, paint, faucets, toilets, HVAC, water heater, etc) and plan on replacing all of it at X years. 

The following are the task.1- install backerboad on all 4 walls.2- install toilet seat3- install single vanity4- floor tiles( area= 4 x8)5- Tiles on all 4 walls6- paint cieling.I am just looking for a ball park labor hours required if all work is done by a single experienced person.

If the home has been vacant for a year or more, I would plan to replace every fixture in the house and re-seat toilets as rubber O-Rings can shrink or crack and wax can freeze.

The states we operate in do not like us charging the security deposit for cleaning we do ourselves, so when I walk in and it's beyond what I consider normal, I hire out to a company that charges about $100 for normal cleaning, then separates the "Excessive cleaning" on the bill, adding whatever additional time it took and why, like oven cleaning, excessive grease, extra attention in the bathrooms like dirty shower stall, toilet stain removal, etc.  

Everything from flooded toilets, rent collection, and tenant screening has been a powerful learning experience!

Maybe offering to move them and a reference is better.I know of several situations in Massachusetts where Tenant/Owners have squatted for at least 8 years;-(

Came home to dirty water splashes all over the walls and toilet.