I use a posting ID. All you need to do is use a different email address (get a free one like Hotmail or Yahoo if you don't have another one) and create a new account. I haven't set anything up in this ID because I never plan to use it for buying or selling. What I mean is, I haven't given eBay my address, phone number, linked it with PayPal or anything like that. I think all they have is my name and email address.

I use the forums in a different browser to my selling accounts. That way I don't forget and accidentally log in using one of those accounts. It also means the selling accounts can remain logged in. I have my accounts open in Chrome and Firefox and I access th forums using IE.

You can use any name you like that is available. That way you can keep the name you want to call your selling account available for that. If you're going to use a name similar to what you plan to use for selling, then it kind of defeats the purpose of having an anonymous posting ID.