Although very uncomfortable for me, I leveraged my friends for their parents who owned homes (especially the ones I've already met). 

I'd routinely get electrical work on past homes I've owned at prices my neighbors were "suprised I'd gotten" once I got the bid, questioned the numbers (if high), and mentioned my ex is also an electrician (who doesn't live near me)."

Keep in mind- it might be uncomfortable, but you and your GC are partners in this deal- you both want the same thing, to win and make money.

-My website is frequented by both agents and buyers routinely.

Seeing them in person revealed they were in a large project style complex that I was uncomfortable investing in..  

Additionally, if you expect to replace something more than once every ten years, you can viably utilize the Routine Maintenance Safe Harbor and  expense the property in the current year.

Make sure you disclose your lack of ability to refinance properties for a while to the sellers though so they understand the risks involved.If you can't widen your search or are uncomfortable disclosing the risks to the owner finance sellers then I would err on the side of buying.

He trusts me enough to just have a joint account, but I'm a bit uncomfortable that it doesn't offer him any protection.Should I just put both our businesses on the offer and the proof of funds would just be from his business?

It's quite obvious that you don't wear a suit all the time if you look uncomfortable in it.

Some of my guys are selling to them routinely.