What is a fair offer to make to that GC, and what kind of deal should I not accept?

Are you saying DMM is acceptable because other methods CAN fail too?

Even a contractor with 30+ years of experience only knows what they know - so, they may not know the most cost-effective solution:(5) Political trends that may lead to more controls on landlords - being forced to accept S8, not being able to deny for evictions, rent control, etc.

I don't have a partner and the most important thing the program was able to give me was the assurance I had picked a good market, lender, teams and execute my business with an already tested system/processes.

It was suficient/accepted by the lender that granted the mortgage for the duplex, so I did not anticipate running into this issue trying to get the heloc.

However, the seller decided to hold off on accepting my offer since the property had only been on the market for 7 days and they wanted to entertain other offers.This experience made me realize the importance of paying attention to the number of days a property has been on the market.

Tenant can still pay rent, late fees, and other penalties in full and get back into my good graces, but I do not waive any fees, accept payments, etc.

Depending on the construction of the building (block or stick, etc), you will want to test the connection strength.  

We didn’t accept the payment and requested proper payment.

They are the professional and should have told me what products were acceptable and what were not so they need to accept at least some responsibility.