I don't think it will make a difference, but this could be his logic behind his response. A gold seller trades multiple clients a day which could somehow trigger something where as the mule would have only traded the seller and the account he wants his gp on.
Yeah, I've had this happen a few times. First time it happened I got a gold farmer RWT ban, and all the other times I received a macro major ban (on a non botted mule on my home ip)
Proxies would be a better option. It gives you the opportunity to run multiple bots on different ip's. What are you doing with your rc accounts? Abyss?