Hi Lance,
I have built and pre sold homes while under construction without being represented by a seller's agent. However, I did pay a small $400-$500 dollar fee to Purple Bricks (Canadian company) which is a service that gives me MLS exposure to sell independently.
Seeing as most people looking on the MLS are working with a buyers agent I welcomed these agents in on the deal for 2% commission. 2% commission + $500 service fee outweighs giving up 4-5% commission on the sale of your home in my opinion. Plus it is like free market research selling privately as you will likely be showing buyers and agents the home directly giving you quality feedback so you know what to add or remove on your next build.
As for Facebook, Instagram, Craigslist, etc it is possible to find buyers but obviously harder. It doesn't cost buyers to use an agent when purchasing a home so why wouldn't they use their service? I'd say stick to your guns and continue to sell on your own but be prepared to give up some commission.
Cheers!