Recently I've had a lot of counter offers (and seller multiple counter offers) that have requested my buyers' "highest and best" offer. Rather than give a number and other details, they're just asking for the best that the buyers are willing to do.
I think it's a terrible practice:
(1) It gives no guidance or direction - the buyers are literally shooting in the target without any sort of target.
(2) It is lazy - the seller and/or agent aren't being professional, aren't laying out the preferred seller response to the buyers' offer, and just skipping right to a "give us your best shot" bottom line. It's the brokers job to communicate and do any necessary work.
(3) It starts the escrow process with a bad feeling - no one likes to think that they're the loser in a negotiation and a "highest and best" is not a win-win approach. Furthermore, as an escrow is a multi-step journey, squeezing all of the goodwill-jelly out of the donut in the first step is NOT wise - the buyer is more likely to cancel or, at minimum, if something else comes up along the way, there is no goodwill reserve from which to draw.
Better: give a number, preferred terms, and negotiate from there. Leave "OBO" to Facebook marketplace or Craig's List...