@Andy Chen, insist on each side having representation like an agent or lawyer and have any agreement notarized.

If they accepted your offer to fill up their little plastic can, they were most likely genuine, but many of them insisted on get the money and "filling up themselfs"

Even knowing this, my buyer was insisting on making a financed offer at $420k.

However, he has insisted on an hourly rate (which in hindsight I should not have agreed to) and keeps expanding the scope of the project, which admittedly was ill-defined by me to begin with.

But hands down, as long as you are getting educated FOR FREE I would personally insist you to take as much advantage of that as possible.

He insisted that this was possible and made a commitment to me while shoving the buyers agreement in my face. 

Joel, I didn't know about defeasance penalties, but that would explain why this seller does insist that the new buyer assume the loan. 

( I would insist on a 3rd party escrow company making payments on his behalf).2.  

Most communication is done by phone and electronic files (spreadsheets, QB files, pdfs, etc.)I insisted on a local accountant for years, and while I got what I asked for, it wasn't a good situation for me. 

I insist on it & I like it through my broker so I know when its due & if its cancelled.I have one that I pay the annual $55 because she is older & has a large aging dog.