You could do a "right to continued marketing clause" in the contract if you do not want to put hardly any skin (money) in the deal.The seller sounds evasive some and that means they are usually hiding something.

I put my rentals on mls but hide the lockbox on the side of the house, and no sign.

This will reduce defaults as most investors know them from past years (unless they had less than a 10% default rate as I did due to qualifying buyers).If you read what I have said on wraps, it is not necessary to hide your deals, disclose as I have mentioned before and the due on sale and other issues become irrlevant..You have been thinking outside the box, that's great.

Either they were trying to hide it.....which would cause me to pass on it.......or this is some sort of joke.

I may approach the situation differently if I thought there was major damage they are trying to hide. 

There are more available  than my company could ever get to on our own and I know there are hundreds of investors seeking these little gold bars that are hiding in the long uncut grass in neighborhoods all over the country.Good luckJim

When I started investing in real estate I would rather hide expenses than income. 

Usually bad tenants hide their short comings from perspective landlords. 

He also claims that he told the seller's agent about this but that he's hiding this from potential buyers, but he's telling anyone he sees touring the house about it.  

They are obviously hiding something and starting out hiding things isn't a great way to start any type relationship.