The denizens of Leng may be good traders, but sometimes you want to bargain with someone who doesn’t hail from a nightmare realm. Thankfully there’s the mercanes. Originally born as the arcane in 2e AD&D’s Spelljammer, and rechristened as mercane in 3.0/3.5, Pathfinder’s mercanes have gained some eyes and lost some fingers (and the secret chest ability is a classy touch).
First and foremost, mercanes are just plain useful—when players want to do magical item shopping that threatens to warp the economy of the local city, mercanes are a plausible way to keep them happy. They’re also an easy jumping off point for planar or interplanetary adventures and plot hooks.
But the real delight is deciding how you want to play your mercanes. In Spelljammer (if I’m recalling right) they were a secretive, unctuous lot who held a monopoly over spelljamming technology. They’d also work well as fantasy Ferengi for all you Quark fans out there, or as an interstellar crime family (or families, possibly dueling) à la The Godfather. Since Pathfinder’s daemons are far less mercenary than (A)D&D’s yugoloths, mercanes might step in as the arms dealers of your campaign’s Blood War—picture Robert Downey, Jr., in Iron Man, sans the moral awakening.
In other words, have fun.
To slay a fiendish dragon, adventurers need a specific enchanted sword. But the noble djinni who owns it is not inclined to part with it. After their failed audience, a mercane approaches the adventurers. He can get the sword, he claims, provided they retrieve a certain item or two for him. Of course, getting the item will not be easy, especially since an azer thief-taker in service to an efreeti “accidentally” overheard the whole exchange.
Mercanes and denizens of Leng seem to almost studiously avoid each other. But the movement of strange living books of magic bound in darkmantle skins and rubies flooding the world’s markets seem to indicate a brewing trade war.
Mercanes are reliable brokers, but not always honest ones. (Though they may be lawful neutral, a contract isn’t a contract unless it’s signed, and local laws may of course vary by jurisdiction.) When adventurers win an auction despite a mercane’s attempt to rig it, he calls on his xorn mercenaries and a wyrwood bodyguard (see the Advanced Race Guide) to catch them before they make it to the safety of their planeskimmer.
—Pathfinder Bestiary 2 188