Quote Originally Posted by Didz
NOTE: AI controlled merchants only perform hostile takeovers against merchants that are actively trading. So, moving a merchant off the trade resource will protect it from enemy merchants.

From my latest patched game, this is no longer true. Merchants on resources will "attack" other merchants who are adjacent to those resources but not trading. I can't say if that means they'll attack well off resources, as I've not seen that (and tend to play merchant-light games as England). Lost a 9-star to a lucky 5-star venetian merchant the other day like this though, I swear those venetian merchants have ungodly luck...