First Owner-Carry Deal in 10's of Thousands of Wholesale Mailers?

[Burt L.]

Had a call this morning from a fellow with two larger duplexes on the same lot, in a strong rental market and principle amount well under market price.  I bit usual layout as its set back from the street with its own access lane and backs to a large apartment building and has taller wood fencing, but the owner has lived there for 12 years and is 73 now and tired of playing landlord with his neighbors/tenants - he has the usual tenant adventures going on right now, such as an eviction and probably isn't a thorough tenant screener. The lot is 21,000 ft.

He has said he has another offer to owner-carry but doesn't like those terms and especially a 30 year carry at his current age,  and can I do better? Of course I don't want a back and forth auction type of scenario. 

 The other party offered him $40K down and a rate of 4.2% for the first 5 years, and then 10% after that, fully amortizing after 30 years. 

He wants a little down more down payment and more income in his 70's while he gets around better. Says the 10% sounds good later, but I doubt he will ever get that, and I suspect they will cash him out at five years or so, but I dont know that offering skepticism on that is helpful. He says 30 years is too long a term  and doesn't want his heirs to have to continue to deal with this. 

Looks like I increase the down payment and the initial interest rate, but certainly don't want to pay 10% after that either. Perhaps 5 years at 5.5% with more down payment, then switch to a remaining 25 year amort at a higher rate, with a balloon at year 20? There are so many ways to approach it and I don't often go deep into the amortization schedules. More than five years before the payment increased dramatically would be helpful though. 

Never had an owner carry before, after many tens of thousands of wholesaling mailers. Looks like a good one - would others have any suggestions on how to structure this better and meet his needs? I am meeting with him tomorrow night; the property is owned free and clear.