Nobody can really know how Jagex really tracks bots and stuff, but in terms of programming it needs just little effort for Jagex to know about many accounts that logged in from the same IP in a short period of time. So they probably know about it.
Can they ban you because you traded with another account in the same IP? No. But what if they really know this other account is a bot? I still don't think they'll ban your main because of that. This is not a common banning method and, as @Cystic said, if you're not trading a really really large amount of money (1B+) it shouldn't be a major concern. You should read the rules of Runescape if you want to be sure if your main account can get banned.
But the thing is: if it's easy for you to set it up, I'd do it through a proxy, since this is the only way "100%" untraceable. If you have no idea about how to start doing this, just keep doing what you do and you should't have any trouble in 99,9% of the times.