That's when I noticed a pattern in the advice I was getting

General Contractors do know how to hire subcontractors to build a house for 50-60% of the selling price... because that's their job; but they don't know how to obtain funding to pay for the construction costs. They get that money from their clients.
Mortgage Brokers do know how to get no-down-payment loans that pay for construction projects... because that's their job; but they don't know how to build a house. They leave that to the General Contractors.
Real Estate Agents do know how to buy property at big discounts... because they can "grab" the best deals before they ever reach the marketplace; but they don't know how to structure a financing deal, so that the buyer does not have to make payments. That's not their concern... the broker steps out of the picture once the sale is completed.
Real Estate Investors do know how to structure financing deals so that they can buy property without having to make ANY payments out of their own pocket, because that's their business; but they don't know how to find discount property to build it on... they have to rely on brokers or agents to get them property, usually at premium prices.