It's a good question. Here's what I shared with you by PM, and it applies for anyone:
As long as you don't mention ANYTHING about your ebay ads or try to solicit business here, you don't need to register. But, registration is easy, so I encourage you to do it anyway, as it might drive more business your way.
By 'anything', I mean: when I see people trying to stealth vend, I don't think it's fair to the registered vendors or the buying public, so it gets enforced. You can't even make a casual, off-hand mention like: 'oh, I might have one of those, PM me' or 'I think I'm listing one on ebay right now, just search there for xxxxx'. That's not cool, and will get called out as stealth vending.
So, the easiest and best thing for all parties if in doubt is to just register as a vendor.