Since no one have answered this question, then I'll. Banker in Norrath are nothing to do with the "Merchant" fraction.They are to do with the fracion of "Anti-Mage" instead. If you really want to raise the faction of Anti-Mage, you can do the skeleton bonechip quest in Felwithe, but before you start, I'm telling you that it will waste up your life time to get the fraction from threatning to indifferently, long and boring.....I've tried it.
I've seen the Brazen Brass Kilij quest gives Merchant faction. I dont know for sure, but the banker might be on this faction. Be a TON of work to find out for sure.
theres a quest in the emerald warriors where you turn in a runied wolf pelt, wasp wing, bat fur, and spiderling eye, it increases your merchant faction, but i dont know if the banker is considered a merchant, i have done this quest about 30 times on my troll agnostic warrior and im still kos