In order to avoid abuse, there is several simple rules to follow and these rules will be enforced by the moderators by a kick of the guilty merchand.
The merchand mode is done to sell some items not to occupy some places without anything to sell and not to annoy other players.

It is then forbbiden to :

place a merchand in front of a map plot, building plot or by any means to bother others players movement

block a merchand place with outrageous priced item (even if your merchand mode contains several good priced items)

sell your merchand place. this way as every Out of game buying that doesn't use the exchange interface will not permit to access to the support if you have problems
In a more general way, every attitude that try to bother the game, the players or the admins will be sanctionned

Good Games and Good selling to all