So I've talked to some people about building a wholesale business and they say network with real estate agents and investors.

Real Estate Agent?

My team has agents in TN and in 20 STR-friendly markets across the US. 

A great investor focused agent, coupled with a great PM, can get returns in a bad market if they know what they are doing.Investors should pick market based on barrier to entry and their available Capital and their strategy. 

Will appraise over our rock bottom selling price of $500k but buyer is "making the case " that he only will qualify for $490k, DP included. 

I am an agent and 2x house hacker just north of Boston.

An agent gave you each of those quotes. 

There were no agents involved and an attorney drew up the papers.

I'm desperately searching for a financing option for my spec homes that will give me better terms than the 10-12% interest plus $10k closing costs that my current HML is giving me.I tried doing buyer-financed, but they haven't been selling very well (although I really haven't waited long, I'm just impatient).

If you have a Buyer Broker Agreement in place with your agent, it may include the language that says all inquiries go through the agent, as well as what amount of compensation is due to them with any purchase you make as their client.