Wrong it is done fairly often. Its not rocket science but it isnt without risks either. It can go well and you can make out but it can also go poorly and you can get screwed. It just depends upon upon your risk tolerance.
A good experienced agent can take the pants off a lesser skilled agent. Last week I got in a contractual tussle with an agent up in OC who thought she was hot stuff. She pissed me off enough to make me want her to pay for my aggravation. I cant explain all the details but she basically was left with the choice of giving up $2,000 of her commission or devasting her client who would have fired her. She deserved it and I would never do that to someone who didnt really deserve that. Other experienced agents might not be so kind.