Let's say you have your own main, you do skilling/questing services, firecapes or whatever. Customers account gets banned, are you at any risk on your main?
no, even if you bot on your pure and play legit on your main, your main account will not be affected by this.
It's highly variable. Sometimes they ban all the accounts associated with the IP, sometimes they don't. Nobody here can give you an answer one way or another. If you don't want to risk your main getting banned, don't break their rules.
Yes obviously wouldn't break the rules since the accounts aren't mine, let's just say a customer of mine has been botting on the account and it gets banned while I have access to it, do I have any risk?