I have the same questions on this.

If we're just small time sellers trying to get rid of stuff, then it doesn't make sense to register ourselves as a Business, since we'll then have to pay for registration as well as do the accounts, taxation etc.

I've gone through the SSM website, and although it's very helpful in telling you how to register and all that, I couldn't find anything on who should be registering.

We'll probably have to inquire with SSM ourselves, since I believe most sellers don't know about this issue (I mean, how many blogshops do you see who registered?)