0xp This looks like a fantasy translation of a scam that was in the news a few years back, in which the scammer would write out a check, coat it with a mild acidic solution, and then cash it at a local bank. Mild acids have been used for a long time to erase parts of documents, but in this case the check would be soaked in enough of the stuff that within a couple of hours it would turn to illegible paper mush (the hope being, I suppose, that what was left of the check couldn't be used as evidence).

The backstory doesn't do enough. As written, the nameless Merchant of Kintro would be sharing a bunk with a family of dungeon rats within days, shortly after the Baron's third son bought one of these necklaces for his mistress. Either the Merchant could have a motivation (enough to risk facing the Baron's justice), or the necklace could be a more common item...

... If as few as half a dozen of these necklaces, or other similar "ghost-goods", were found out to be in the city, the customs of the area might change. Perhaps a jeweler would present his goods to the customer for inspection, and then they would settle down and discuss the price over a leisurely three-hour lunch. If the jewelry disappears during the lunch, the jeweler goes to prison.

(Plot hook: a jeweler friend of the PCs has been arrested for this sort of fraud. He was framed by a servant, or a thief disguised as a servant, who stole the necklace during the three-hour wait.)