Well I don't see the point of going overboard about that.
We have a number of members selling stuff, who include Reef, Steve, and Brendan. If the avatar or sig or whatever informs people of this, from where I stand, this is useful information to the members.
Also, when there is a discussion on some product, in particular a new one that nobody has any experience with as yet, I find it silly that the vendor is not allowed to join the thread to add information, and perhaps correct misperceptions that may be in evidence, again, that would be a useful service to the members.
It's where we have competing vendors having a slanging match, then THAT may be a problem. However if the rules are to be properly enforced, then the slanging matches can be stopped, and vendors allowed to add constructive comment, then that must be a win for everybody, vendors and the rest of us.