A flat fee can be good, and with $100/unit in our area you are highly likely to cover the bill and even have money left over, but you do run some risk of paying a difference. 

The leftover stays and reduces the principal balance.

If you end up with any leftover gain, you could also do a 1031 exchange and defer the remaining tax. 

Whatever is left over goes to rent. 

There have been a number of syndications that have quit paying dividends as of late because they were tied into variable interest rate financing, and as the Fed raised rates there wasn’t enough money left over to pay dividends.  

Instead of ceramic tile on the shower walls, I had left over cement board siding from a previous job..

Where little Tim and Jenny can get a good education, the family can live in a modest house, and still have enough left over to save for retirement?  

Cashflow is simply what is left over after an asset generates revenue and pays all of its expenses.

You'd have one property and probably have $60k+ left over to keep buying rentals.

There was $700,000 of depreciation leftover at the time of the exchange (aka “carryover basis”).