Actually, depending on how it's done, I think Trader is the most difficult. Especially starting out...
Traders are insanely easy to twink. But extremely difficult to start brand new. Almost everything the trader does depends on them doing with while buffed from divest/plunder. That means always needing weapons/nanos above your current level. That means always having higher costs than other players/professions your level.
Next is related to the buffed status. We can argue for days about whether or not nanoresist works on players. But it definately works on mobs. Having a mob chain resist a Plunder 6-8 times isn't as uncommon as I'd like. And any trader that depends on being buffed by both Divest and Plunder to do anything can land in immediate hot water.
Next is a trader is a born NCU hog. Our own buffs eat NCUs for breakfast. While we have complit buffs to assist in wearing better ncu equipment earlier than other professions, see the part about credits vs level. And still I think I was happier than most fixers about them getting NCU buff nanos
Finally, a trader is the most hated profession by others IMO. We've been walking hate magnets since the 1st trader hit another player with a Ransack in PvP. Even our Arch Enemies, the Doctors, have sought our head on a plate occasionally . And they should be pacifists considering they're healers. Nevermind what they do to us with an init debuff.
Come be a Trader, one of the most misunderstood professions on Rubi-Ka. Most of the people that start traders believing in the 'uber' mythos prolly quit in a very short time after discovering what a cast iron pain in the ass it is to be a good trader, including the twinks