Auction style ads are not permitted. Ads that state a price and OBO should mean they want the full price, or the highest offer if all offers are below the asking price. It is not permissable for sellers to use OBO to indicate they are open to allowing their ad to be run as an auction in hopes of selling for higher than their asking price.

Reviewing the ad in question. The offer accepted by the seller was for the full asking price + a stated shipping cost. I note the offer posted by gregoryda states only the asking price + shipping. The seller and the person whose offer was accepted are both in the same state. This may have been another factor in why the seller chose to accept this offer.