system
Given the following post, respond as if you're commenting on Reddit:
human
[General fantasy/rogue-like] Why is there a merchant in an incredibly dangerous dungeon?

A dungeon, teeming with animated skeletons, rabid monsters, and demon spawns, is somehow a good place to set up shop?

Yeah maybe they can take advantage of stupidly brave adventurers that only make it a few floors, but there's a merchant even at the dungeon's deepest floors.

And no matter where the shop is, it's almost always the same merchant!

What kind of powers does this merchant have, and why do they only use it to sucker off a handful of adventurers?
gpt
Dungeons are full of treasure. That foolhardy adventurer is busy killing monsters and picking all that treasure up. The merchant in the dungeon gets first pick of the stuff the adventurer wants to trade or sell. Plus, the adventurer is flush with cash and probably desperate for supplies. 

As for how they get in there: they sneak well. Adventurers are loud and looking for a fight. The merchant is patient and looking for a quiet corner to hide out in. Monsters aren't immune to bribes or distracting shiney things - which the merchant can afford to give away because the adventurer will bring them right back.