If you need or want to have an auction in your Ptolus game to pry a little cash from the characters or to introduce something into the game, some of that work has already been handled for you as far back as Dungeon Magazine issue 13.
A retiring wizard has offered up a bunch of stuff to be auctioned off, raising funds for charity. All his really good stuff was taken care of separately. The money raised from the items in this auction is to be divided between orphanages maybe in North Market, soup kitchens like Saint Dayra's near the Warrens, etc.
The auction is taking place in a large warehouse which could be on the edge of the Katterwood neighborhood of Midtown, and is run by a halfling and his adopted half-orc daughter. Stereotype? Maybe? She likes the finer things, dresses well, wears make-up well, etc. Sure she's her father's body guard, but she could easily become a PCs love interest.
The adopted daughter was picked on and bullied a lot as a kid (it says so in the adventure). She's been taught how to handle it. Her close friends and co-workers will pipe up if someone tries it now, but how would she act if a PC was presumptuous enough to come to her defense? Could she see it as an insult implying she can't take care of herself?
There's really not a connected adventure here, just an auction with possible jumping off ideas. Maybe someone wants to steal the funds. Perhaps someone of importance is in attendance and an attempt is made on their life. Will there be other arcane spellcasters there? Most likely, and who steps in to break up a bunch of rowdy wizards? Plenty of potential for hooks.
A possibility that presents itself would be introducing an item of your own, with its own hooks, especially if it doesn't belong in the auction and doesn't belong to the wizard. How'd it get there? Who introduced it and why?
Of the items in the auction that caught my eye as having potential to make a DM work a little harder, but not be game breaking are the Location Tags. Attach them to something and if you need to find it call out the name of the item (example used was slippers). The 1" square tag then chirps like a cricket until found and the word Ah-Ha! is exclaimed. They can serve as a less effective version of Locate Object.
Each item in the auction has a listed starting bid price and there's a percentile roll mechanic that can be used to see how bidding proceeds. You can of course make up your own method.
There's one very expensive 5,000 gold piece painting that has something to do with a Noble House, perhaps Abbercombe, which is a defunct house. Lord Zavere of Castle Shard might be very interested in this particular item.
In some campaigns having too much loot in PC hands can act as a demotivator. Here's another way to drain a little gold without it feeling like unfair DM fiat. Players often enjoy the shopping aspect in the game, especially when it deals with magic, and auctions are a competitive way to shop. Competition drives action.