It is incredibly common in transactions more complicated than buying milk for both parties to communicate over time the many and varied factors that could effect forming a final agreement including both parties thoughts on price without intending to or forming a final agreement then and there or listing every possible contingency in every single informal communique.

The salesman and the buyer discuss the merits of the car one says they think they could pay 25000 and other 28000 but the buyer intends on test driving and having it checked out mechanically. Meanwhile the seller expects the buyer to have acceptable credit, sufficient down.

Whereas price could enter the discussion along with other factors both parties expect there to be a formal step in which paperwork is signed which actuates the sale. This could even in less formal situations be a handshake and a check but the difference between one and the other is clearly expressed intent to complete the sale.