The assumption doing the most work in that negotiation is that the contract seller's ARV matters. It does not. Your buyer's ARV is the only number that closes a deal, and your six comps from inside the subdivision are the sharper dataset. A pond-back comparable two streets over is not a subdivision comp, it is a lifestyle premium in a different micro-market. That distinction is not always obvious to someone who sourced the number from Zillow.
The spread math here is the real pressure point. Your buyer moves on anything under $35k. At $187k ARV and a standard 70% acquisition target, that ceiling sits around $131k before repairs, lower with any meaningful rehab budget. You were already working with $165k, which suggests the buyer was carrying limited rehab assumptions or the ARV tolerance was already stretched. At $172k acquisition the spread collapses, and your buyer knows it even if the contract seller does not.
Four days is the damage you did not mention. A ready buyer does not stay ready. The Akron deal is real competition now, and if he ties up that contract your deal window closes regardless of whether the seller moves on price. Dispo-only economics depend on the match being fast. Once the buyer's attention shifts, you are not negotiating anymore, you are starting over with a different buyer at a different price expectation.
The risk that was not in your post: do you have a second buyer at a lower acquisition number who could absorb this deal at $160k or below? If yes, that changes the conversation with the seller entirely. You bring a real offer rather than a standoff. If no, the buyer list is thinner than the speed advantage requires, and this scenario will repeat.
What does your buyer list look like for this price range and market, and do you hold verified proof of funds before a deal goes out?