Not to totally stir the pot, but the Law dictionary clearly states three factors that make any agreement in a verbal fashion very difficult to stand up in court.
1. Reasonable... If an associate says they will sell it for less than cost out of mistake or misunderstanding, the terms would be considered unreasonable. This also factors context. They may mean used, B stock, or applying other coupons and offers. And you can't expect them to sell you something for less than cost, as that would be unreasonable.
2. Equitable... Refer to point 1 about selling below cost. If both parties can't have a reasonable and equitable trade, the verbal agreement is meaningless. Especially if the context is misconstrued.
3. Conscionable... The seller has to know what they are agreeing to as much as the buyer, and both parties have to be fair and honest in that trade. For example, if you know the associate misquoted the price and yet you stuck it to him anyway, that would be unconscionable. Conversely, if the associate sold you a product for an unreasonably low price and to make it happen they changed product info or cheated the system to make the sale, that too would be unfair to their employer. It would not be equitable.
In eBay transactions it is different. The seller has the ability to amend, end, or create parameters for a sale to occur. If they fail to do so and you win an auction, this puts the ball in the buyer's court. The entire transaction would have been made in good faith. There are punishments or sanctions if you try and renege on a transaction on eBay. The contract is more or less written in this case and very hards to argue in a legal dispute.
I would never be so crass as to get litigious over a clear misunderstanding of policy, abilities, or perhaps even level of good faith. If a seller is really trying to bend things to make a sale work out and they can't pull it off, why would you try and get litigious for it?
Everything I have ever truly wanted I have gotten. From guitars, amps motorcycles, and a wife, to what I eat and where I poop, If I truly wanted it, I have gotten it. If I have to pay more than it's worth, or I have to wait till the tides are in my favor. My thought process has always been that if I made it this long without it, having it now won't change yesterday. Keep looking and keep saving, if you truly want it, you will get it.