Buyers these days do a lot of their own searching. If a buyer finds the listing on Zillow via MLS, it won't stop them from viewing the house even if they have an agent.
Once they view the house, the owner could convince them to ditch the agent. I mean honestly, what does the average agent do for a client? Not very much.
Most Buyer Agency agreements operate on the basis of "if we show a house to you, and you buy it, we are owed a commission regardless of if you terminate the agreement afterwards". Now, typically a real estate agent isn't about to sue their clients if they purchase FSBO, since that would mean suing them for a 2.5 or 3% commission the seller wasn't even offering to the buyer agent, but it does mean that you can't get agent 1 to show a house, then switch to another agent, without agent 1 getting paid.
Do buyer agent agreements require you buy a house through them even if you find the house and view the house and negotiate the price with the seller yourself?
(I’ve never relied on an agent for these things, I did everything myself when buying my first/only house)
If I was working with an agent, I’m sure they’d discourage me from that listing, but as a seller in a reasonable market, I’m willing to give up a few possible buyers to save 5-6% on a 7-figure transaction. (I’ve also seen FSBOs that offer X% to buyer agents.)
I will say that agents did do some work to make the transaction complete on both of my house purchases. Negotiations after the inspection can be tense and a good agent can help both sides get to the closing table.
This is exactly my experience. In shopping for my first house, I had a clear idea of what I wanted and a budget that matched that and the first four agents I worked with were nearly useless. (This was before web-MLS was a thing.) The fifth was a breath of fresh air and I would happily use them again.