Seller in my target block wants to list with zero buyer-agent compensation advertised anywhere

The way I'd frame it is as a spread, not a principle. Offering 2.5 percent on $520k is $13,000. Ask what the alternative costs. If refusing it adds three weeks on market, you're carrying taxes, insurance, utilities and interest on whatever debt sits on the house, plus the risk that a stale listing invites a price conversation you didn't want. On a house like that I'd guess carrying cost runs somewhere near $2,800 a month, so three weeks is maybe $2,000 of hard cost. That alone doesn't beat $13,000.

What beats it is the price effect. If the buyer pool narrows to people who can write a check for their own agent on top of down payment and closing costs, and if that shaves two percent off the best offer, that's $10,400, and you're at breakeven before you count the extra weeks. So the whole decision rests on one assumption: how many qualified buyers in that specific price band are cash-constrained at closing. In a first-time-buyer band it's most of them. At $2M it's almost none.

I'd also want to know what her agent has to get in writing. Under the new rules the listing agent has to disclose and get the seller's written approval for any buyer-side compensation offered, and the mechanics of that paperwork vary by state, so she should confirm with her agent and her attorney where that applies. Offering nothing doesn't remove the conversation, it just makes it a one-line conversation.

The thing I'd watch is what happens at the showing request stage rather than at the offer stage. I've been sitting in on listing consultations while I build out my own service side, and the agents who are having the smoothest time with this are the ones who set the seller's expectation up front: we'll list with nothing published, and if a buyer's agent comes to us asking for compensation as part of an offer, we treat it as a term to negotiate like the closing date or the inspection period. That way the seller isn't paying $13,000 to everybody, she's paying it once, to the one buyer who actually got to the table, and only if that offer is the best one net.

Sextant's spread math is the right shape. What it misses is that compensation is now a negotiable term inside the offer rather than a posted number, and a seller who understands that has more room than a seller choosing between all or nothing before the first showing.

What I'd tell your neighbor to ask her agent: how many of your last ten sales had buyer-side compensation appear as a term in the offer, and what did you net out at. If the agent can't answer that from memory, that tells you something too.

Lantern's version is the one I'd use. Negotiate it in the offer, don't decide it in advance, don't publish a number.