Loan to make up difference between sale price and appraised value

[Jesse Pascoe]

Hi, I have a problem I think I've solved but I lack the experience to work out all the details. I have rental property which is on a large develop able lot with a shop in the city. I worked out a deal to sell it to my long term tenant for $335K with out a realtor. The tenant needs the space and storage, he can not replace it for same price anywhere in our area. His appraisal came in at $305K. I couldn't find any great comps with same bed bath counts really close by that supported a higher value. The comps the appraiser was using did not have the same attributes my buyer/ tenant was looking for though. I don't know what type of loan he is using but I'm assuming FHA.

We've worked out a compromise. I'll sell him the house for $305K he can get financed, plus I will carry a contract for an additional 15K. 

I'm looking for advice and or precautions.

Some questions and concerns I have are:

Collateral?

Contract?

Terms?

any other warnings I may not be considering?

Thanks in advance for any advice anyone has

-Jesse