I'm sure Wire was aware of this issue. But I'm also sure that no one here depicted the real purpose of Thieves Guild. They avoid any contact with guards. They can steal, of course, but they also manage to lockpick cars/caravans, to be burglars or to set traps when someone asks them (if they are offered money).
Also, keep in mind this is mainly a roleplay faction, if I understood well. They do not want to make profit above all.