Two reasonable adults, seller & buyer, can arrive at a mutually beneficial agreement without anyone in between them.
Without anyone in between them, there is an inherent advantage in the marketplace, for both parties.
That advantage is a deeply discounted, great deal, price for the buyer, and for the seller it is the leverage to choose the strongest buyer (i.e. strongest funds) a shorter number of days on market, an easier transaction with a motivated buyer and a good net return for equity.
The nature of this dynamic facilitates a different kind of transaction. It is one where neither party feels “pitted” against the other, since there is so much obvious advantage to both. This, then, also diminishes the impulse to ‘sweat the small stuff’ and/or ‘drag feet’.
With high motivations and no one feeling like they ‘might be getting screwed’, in conjunction with clear and accurate transaction tools, the strength of a FSBO deal being brought to completion skyrockets.

Think of it this way, 90%+ of the other sellers are using agents. This usually costs them between 5-6%, which is reflected in their selling price. By doing that, the other sellers have given you, the FSBO seller, the single most powerful marketing advantage over them that exists – a significantly lower price. The market has not given you this advantage; it is the other sellers who have given it to you. And yet your net proceeds at closing can be comparable or more than theirs. Moreover, it is a strong position in relation to the buyer for terms, etc.

Plus you get the lifetime benefit of actually learning the process.

Q. “What if a buyer has an agreement with an agent and they are, therefore, committed to paying out a commission?”

A. Then either you can negotiate cooperation with paying that agent or else the buyer can pay for their decision. However, you may be able to help them pay by agreeing to a higher price and then credit the buyer at the closing or your buyer can simply roll their agent’s fee into their loan. In any case, it must be with full disclosure to their lender. And since you originally priced well below market, the home should be able to easily absorb the 2-3% higher appraisal thereby helping your buyer and their lender.

Of course, as a seller, your strongest buyer is going to simply be a legitimate cash buyer (not a flipper/wholesaler who will want massive discounts).