Who sets up an owner financing deal?

[Thomas B.]

I'm looking at a deal with a retiring landlord. They have a multi unit property which will not qualify for conventional financing. 

We have hammered out an unofficial deal on seller financing.  Who would actually set up the transaction, an accountant, an attorney, both?  Do I need to look around for a specialized real estate attorney or accountant? 

We both know how to work the numbers, but neither of us is familiar with exactly how to go about it from the legal standpoint.  He obviously wants to make sure he gets paid. I want to make sure there can be no funny business if he changes his mind or have the government or his kids try to unwind the transaction if he dies or goes into assisted-living since I believe the seller technically retains title to the house.