Buyer walks because they won't pay more. ...Starting to get the picture here?

If by chance you took pictures of your place before leaving, attach those as well to show it was in good condition. 

That's why supermarkets have so many slip and fall claims, they have the duty to protect the customer from injury in most states, meaning just the fact that it happened is proof of negligence.  

Are you receiving invoices and pictures of all work?

[EXTREME OPTION]The best option I use is, require your PM to provide pictures of repairs needing to be done before it will be approved, and provide pictures after it is done to be paid. 

Added features in a property can identify you, it can be as simple as a custom touch on kitchen cabinets, a key stone arrangement outside, a custom door knocker, an igraved mantel or a decorative feature in landscaping. 

You can read the meter and take a picture of it when yu move in.  

Clearly you don't want to go into it with the plan to learn the business then steal all of their customers but knowing the current owner's end game would be important from the beginning.

In my "day" job, I have 10,000 customers billed for services on a monthly basis.

I currently work in a customer service job, but know it cannot provide for my financial future.