The DC area is one of the lowest cap rate markets in the country.In MoCo you'll generally need a 40-45% down payment currently to have your rent cover your PITI on a standard long term rental.

What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

Before you pay a fee, you should know what that fee pays for and if it is refundable or credited towards closing.

Don't let anyone pull your credit until you ask and have tehse questions answered, or every lender in the whole county will pull your credit. 

If it's too much you can always move your business to small local banks / credit unions but there is another price to be paid.

And if you try to sell it with an old roof, chances are the buyer will want you to give credit or change it.Please make sure these numbers, insurance, tax, rents are actuals.The electrical may have aluminum wiring, which may need to be updated, and some plumbing means none has been done.The value would be can you increase rents when they come due?

One filled out the application but refused to do the credit and background check so i rejected him.

Nevada has the 4th lowest property taxes in the U.S., with no reassessment upon sale, unlike California. 

But not for a typical purchase.Also, remember that the buyer agent cost should be paid by a seller credit, so it isn't additional money that you need to bring to closing.

The interest rates are higher, currently 10-11% but it's interest only and it's a revolving line of credit you can use for anything.