Are you in a hurry to move? The buyer may have interpreted your low season listing as a "motivated seller." I wouldn't do anything extraordinary before the Spring selling season kicks off. Although, you have put yourself at a little disadvantage for this spring--your listing will look old, by then.
Homebuilders are offering mortgage buydowns for their buyers, to keep their prices high. If my own circumstances dictated some out-of-the-box thinking or addressing an offer like this, I would counter with a buydown. Now, that is likely a $30k - $50k item, so $10k over still means nothing. (Either research what it would cost for a house around your price, or offer a flat amount toward a buydown) But offering a buydown helps buyers where they hurt (monthly payments) without getting entangled with them for 30 years. It also makes them go through the mortgage origination process, so someone else--a bank--is vetting them.