Someone needs to be the adult here and stop rules lawyering and looking at this like it's a labor dispute or the group is going to fall apart. It's why most gaming groups only go a couple of sessions before suddenly people have more important things to do on gaming night.
Oh I don't mind players messing up at all. Sometimes very unforseen and interesting circumstances are created.
But in this case we are talking about miscommunication. The players themselves later refer to wanting to investigate the ring; hence it has always been in their mind (and perception of the campaign) that they still had it.
The Ranger first chooses to go to the magic shop, but the rest of the party remind him that they do not have any money for identification spells. He goes to the blacksmith instead.
At the blacksmith (a half-orc they already know from before) he presents the bundled up armor. The blacksmith studies it, making note that the armor is very damaged (from the battles) and it would lower the price. At the mention of the price being lowered, the ranger asks if he can make a int check to learn how much such an armor would go for, he rolls well. The half-orc notices the magical ring and immediately asks "Are you looking to sell the whole thing?" to which the ranger immediately says yes. The blacksmith offers a price, the ranger isn't too sure since it was lower than expected. The blacksmith argues that with the damage would lower the price and he still needed to make a profit. The ranger still seems to have a hard time agreeing. The blacksmith quickly adds that it's money up-front. The ranger agrees.
The ranger then shows the mithral sword, saying it is from an ancient kingdom. The blacksmith offers a price, but the ranger isn't pleased and the blacksmith does not argue and lets him go.
Eh, put Cell Phone Guy in charge for a while. If he's as bad as he's made out, they'll clamor for the old DM.All DMs can play.
Few players want to DM. Because of comments like we see in this comment thread.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.