Collection on Stop Pay while buyer still has Merchandise in Posession

Owner of a pawnshop going out of business. Another pawnshop makes oral agreement to purchase active pawns. Terms of oral agreement are buyer takes active pawns, buyer takes active pager customers, buyer is allowed to advertise on marquee and hang 1 sign directing all customers of out-going pawnshop to buyers location. Buyer inspects all pawn merchandise, delivers to his location, and cuts check accepting the oral agreement. This was on a Monday. On Thursday, delivers a letter by third party stating he has placed a stop payment on check because seller has breached contract. When contacted, buyer states breach was that seller did not verbally direct all customers (pawn or otherwise) to his location only. This was never part of the oral agreement to begin with. Buyer wants Seller to retrieve his merchandise immediately but when seller gets to location, buyer immediately wants a written hold harmless statement plus a statement saying seller has received all goods back prior to actually receiving them. Seller refuses because didn't believe an oral agreemeent should be terminated with written contract, and contacts Department of Consumer Credit which regulates pawn shops. DOCC agrees that buyer has acted in poor-faith but can't enforce anything other than when pawn customers are wanting to pick up their merchandise, buyer has to accept payment for seller until legal issue is resolved. What grounds do we have to stand on? We are in State of Oklahoma.