Former real estate agent, now software engineer. Doing a FSBO (for sale by owner) is as old as time. There's nothing wrong with this approach, but you are limiting your market (and you might therefore be selling at a lower price anyways) and it's highly dependent on your: patience, financial situation, free time, marketing skills, general sales skills, local housing market, tricky property situations, ability to assist buyers with locating financing, handling any objections or mortgage exceptions that come up (including zoning and inspections requirements), etc.

Buyer's agents deserve their 3% perhaps even more than listing agents and it's unfortunate you screwed this agent out of that. It's sort of like stiffing a server on a tip. Buyers are fickle, time consuming, and sometimes demanding. It can take many showings and offers to find a good fit for someone. Sometimes I would work with a client for weeks or months. Many clients would fall through and you'd get $0 for those clients. So you have to average out your earnings with the successes.

There's other things you have to do, too sometimes. Like once I had an FHA financed client and there were certain restrictions about the distance a well could be from the septic tank at the Federal level but they didn't match the requirements at the county level (which were looser). So I had to coordinate with local zoning and the FHA to get an exception for this loan. That was a bigger ordeal than I can explain here.

These online MLS listing services have been around since 2004-2005. They're nothing new. Are there crappy agents? Yeah. Just like any profession. But the profession itself is not going anywhere.