the seller is 100% true. The notion that buyer's agents are "free to the buyer" is comical.
Any moderately intelligent seller with a moderately reasonably agent (and reasonable agency agreement) will happily take a reduced offer from an unrepresented buyer, as it nets out exactly the same to them (i.e. 2.5 or 3% less than you'd otherwise offer, validating that both parties are implicitly agree the true value of the home doesn't include those commissions).
I've only ever had two agents ever put up a fight about it up front. Both were stereotypical toolbag types, and at least one of them I learned was subsequently fired by their seller after being unable to move their house in a ridiculously hot market because of his toolbaggery.
Now whether they'd still try to do shenanigans at closing to hose their seller and snake the entire 6% for themselves and hide behind some automatic dual-agency clause in the contract, is another story...