Comparing these terms to the best financing I've found through a bank ($320k loan, 5.5% fixed for 10 years then refinance, amortized over 25), with same purchase price and down payment, results in a lower monthly payment by $315/mo, plus my principal balance after 10 years of payments through bank financing would be $240,000, compared to the $180,000 balloon that the seller wants at year 10.

What is enticing to one investor might not be for another one, so is a very difficult question to answer with such limited info.Also, I don't have experience with multi-use resorts so I'm not quite sure about what is a "typical" structure used in that niche. 

I'm not sure on 1) how to structure the lending part. the 3-5 yr part for the balance 2) what terms should I set for monthly payments 3) I'm in NY which is a judicial state do I have to use a lawyer 4) what are the risks for the property owner and myself 5) when and from who do I get my assignment fee6) If they have that much cash why not just get a loanThank you in advance for the advice !!!

You may need to amend your tax return if you already filed it but this issue should not be difficult to correct. 

find a properties that would be difficult to finance with traditional lenders because of condition or class of property i.e. zoning or use.

.-$135k remains:---$67,500 (half of balance) due December 2019.---$67,500 (half of balance) due December 2020.-$0 in between. 

My question is; how difficult, or how likely, is it to structure a deal using partial owner financing? 

Might not be a bad idea to balance out your higher risk properties with a few that are much lower risk.

@Karen Emery  how does high mortgage balances work?? 

The guy is worth hundreds of millions, so it's difficult not to take his opinion very seriously--it's making something I was very excited to get into feel like this enormous risk that I won't end up pursuing if I keep getting this lecturing about it.