Other options I'm considering are a $10k down, $30k note, or if he really wants more money, extend the note to 15 years, and higher principal. 

A key thing to consider is whether or not you can cover the holding costs for the duration of the project.

For rental properties, I am open to extending the geographic area to most of Northern Virginia and Southern Maryland.  

For rental properties, I am open to extending the geographic area to most of Northern Virginia and Southern Maryland.

I am going to offer to extend the contract however they must reduce the price for every month that goes by. 

If they walk you take them to court for the duration of the vacancy.I would tell them that they may sub let the unit, they and you may both look for replacements, the sub lease applicants must be approved by you.

I would do that, but I'd be nervous to have to pay several mortgages for an extended period of time if rent didn't show for a certain month(s).

They are also more likely to become life long renters and less likely to become home buyers.I believe credit history is more relevant for merchants who extend credit than for landlords who provide housing to renters.

Before now, my plan and vision didn't extend past the point of paying this house off and turning it into a rental.

Ok, so my son has a situation where a lease was up and he went over to deliver a new lease to extend the tenant's term as he appeared to be a good tenant and found an interesting situation.