In my world I have created a Specific NPC, his name is Bob. Bob is a 90 year old 20th level wizard and has an extreme case of the scatterbrain. Bob runs a magic shop called Bob's Bargain Basement. His store exists in a small demi-plane that has a random chance to attach its door to any empty store front door in the material plane at any given moment. think Howl's Moving Castle style only random based on the size of the city. His inventory is supplied by a magical contract that transports any "lost" magical item from the material plane directly into the store. Bob does not have the time or inclination to organize or identify any of the items in the cramped shop. He organizes his shelves and aisles by item time but the contract stocks the shelves. His magical rings appear on a peg board that is 10 pegs by 15 pegs and stacked 10 rings deep per peg.
If asked what a specific item is he describes the items physical characteristics and is immune to the effects of any item brought to the store by the contract. Since bob has no idea what the item is he has no inclination of what to charge for them. I roll a d100 to determine what percentage he charges for the item of its actual cost. This may seem like a very monty haulish kind of place until you take into account that most intentionally lost items are cursed items. The aisles between the shelves require that any medium sized character wearing med armor or heavier must shuffle sideways down the aisle to avoid knocking items off of the shelves. Any item, normal or cursed, that falls off of a shelf has a percentage chance, usually 40%, to attempt to equip itself to the player.
all that aside, I once made the mistake of allowing the party to search for Bob's at 1:30 in the morning while in the middle of a sugar high and little actual sleep proceeding the marathon game. The players decided to break into 3 2-player teams and "attack" Bob with 3 competing conversations among 6 PCs at the same time. After 20 RL minutes of round robin appraisals, Bob's failed memory checks, bluff attempts and general all around confusion on my part the players walked away with a tidy sum of gear. As well as a purple PC, a gender changed rogue, a male fighter who's hair had been polymorphed into flowering ivy and magically compulsed dwarf. to this day they still chuckle at me when I start on the sugar train.