It is a stupid act to raid the Traders that try to make business for City's in your area
they don't want you to make business, they want their s&d untouched, i'm sure if u went into ts and asked it would be a different story. just remember that nowhere on the map is safe for random traders, one of the harsh realitys of strategus
also S&D is used when u buy/ sell in a fief, it is a limited amount, thats what they were trying to protect it. really your better off joining a faction if u want to play strategus