Is there somesort if merchant guide?

[Mr C.Folt Scruff]

idk if it worth the time transporting this guy half map only to get owned by the local high level merchant

they can also trade slave i think does it contribute to Original city pop increase?

[Jambie Lionheart]

There's no guide persay but the best way to use them against enemy merchants is numbers. Numerically speaking, even if a max level merchant does come a long, you'll beat it eventually, and probably before it pegs out due to old age. The same goes for your own merchants too, of course. That's the short answer.
Thats also how to train merchants up in game too so that you can eventually get a foot hold in your area. Until your merchants reach level six, they're very easy targets for other merchants, unfortunately. Even at level 6+ they're not exactly invincible either.

THe best way to use 'em is in combination with spies and assassins.

You use the spies to find easy target merchants, (because you wanna use them to level up your merchants as quickly as possible), and those that are potential threats to your own merchant and then you use assassins to kill off high ranking enemy merchants in order to protect your newly levelled merchants. Once they get into the higher levels (level 8+), their benefits to your economy will be enourmous. Especially if you have plenty of trade partners. You'll have to root arounda little for the best resources spots to take. They are not created equally. Resources nodes, even of the same type can differ in monetary yield by huge degrees.

If you play as Romans, for instance, amber is a really good resource node to take. Most of those are in and around Germania. But there's a few hundred denarii's worth of difference between the best and worst amber nodes for a 10th level merchant to take. A really good node to take is the amber node in Denmark on the very tip of the continent. Find the rest yourself >: ] Happy hunting.

[Father Damien]

Jambie has provided you will all of the advice you need. But if you see a high level merchant near yours, you can take refuge in the local settlement. They can't buy you out whilst you're trading from the inside. Make sure to buy out Rebel merchants. They become easy pickings and help your merchant level up. I'm sure standing on the specific nodes increases your level too. But someone can correct me if i'm wrong on that. Normally when i play as Rome, i like to send my guys to Egypt. It takes a while but it becomes a great investment.