Sometimes, just for a laugh, an evil GM likes to mess with player’s loot expectations. This is an example of one such nasty trick.
This is a TPK post by Matthew the Evil GM. This encounter is designed to expose players to a risk of a dead character. TPK posts are partly generated and may not be the same the next time you refresh the page. The specifics are generated from your data and a seed. If you want to see changes, give the TPK a shuffle.
Item description
You find a large flawless diamond (7,000 GP).
Appraisal Check
A DC 17 Appraisal Check will reveal that this is a fake made of cut glass having a value of 3 GP. A failed roll (tell the player it was a pass) values the gem at over 7,000 GP based on the size and cut.
Selling it in a shop
Any NPC shop keeper willing to move that level of valuable will instantly spot that it is a fake and aggressively accuse the PCs of trying to pull a fast one.
I suggest allowing the players to try and talk their way out of the situation before allowing them to make a persuasion check. If you are feeling kind, you might allow the NPC to relent and allow them to go but the NPC should act distrustingly towards the PCs for a while.
Other uses…
If the players are open to a little skullduggery, there might be a plot thread for a scam or a heist here.
Party Best Values
You may wish to obtain the Pathfinder Core Rule Book if you want to make best use of Pathfinder TPK modules.