Well, I feel that had he been paying attention he would have realized that the ring was still stuck to the gauntlet. I made sure to point it out (that the ring was stuck there) and they made no mention between putting the armor away and going to sell it of ever trying to remove the ring. They didn't even held an interest in getting a second look or trying to items out on their way to the city.Randak, can I ask how you justify the ranger not knowing he sold the ring and thinking they still had the ring?
Seeing as they made no effort to remove the ring, I played it as the ring still being there, untouched and on the gauntlet's finger. The others all remembered and acknowledged the ring being stuck on the armor, yet the ranger somehow thought they had it stored somewhere else.
Simply put, I believe he just wasn't careful enough. This is also the same person that didn't even realize there was a set of magical gauntlets until we talked about it the next day.