Well another thing would be to have them post under their own name like you seem to be suggesting Timelord, but I am thinking that if they are my agent(s), then they should post under a Nym that I am able to control and that clearly states the relationship.
If they can post from the account, you don't control it

If they make their own account, you can leave neutral (
or if you trust them even positive) feedback stating the relationship. If they quit, you remove (or update) the feedback.
Sharing accounts also means
disclosing IP addresses of all users.
[otherwise it is too ambiguous, too weird, and even likely to have backlash on me, too... and maybe even harder to keep track if there were to be multiple accounts (besides starting out with one)[/quote]
I assume you'll need to keep track of your agents anyway. This way, at least you can distinguish who does what.