Wierd Sub To Deal
I have a situation where I bought a house sub to, the owner was a realtor. He asked me, after explaining to him what's going to happen and how the loan is staying in his name, he asked me if I had any other houses for sale that he may be able to move into. I know I have the deed and the property I got from him is signed sealed and delivered, however, I'm not sure if I want to sell him a house I picked up somewhere else. Even if he could come up with the whatever required down payment I would charge, would you sell a house 'sub to' to a person you bought a house 'sub to' from? Don't forget that he is a realtor. 
No matter the profession, if you dont feel comfortable with the person or their situation, go with your gut feeling. Simply tell them that you dont have any other properties available at this time, but that you will keep him in mind!
Best of Success!
BAMZ