In marketing terms, your ebay seller id is your (brand). In general marketing plenty of focus is usually paid to building a brand, it's what identifies you to the general public.
Aspects such as name, logo design, colours all play a role in developing a strong brand, so as to ensure you can be identified easily in the marketplace.
As for online sales such as ebay, I don't personally place any marketing weight on a sellers id, not unless you are trying to develop or link that to a brand that you already trade under offline.
I would suggest a more general trading name, although I'm sure you can be more creative that seller09 : )
Has the sound of a Chinese scam site!
When trying to find a name that fits in around what you are selling without actually putting you in a box, try looking at where you want to be in 3 years, in 5 years, 10, 20 years.
Which direction do you want to drive your business, and what products would you like to be selling to get you there. Any business is about future planning, having only short term goals usually leads to having short term businesses.
I'm sure quite a lot would be surprised that once you develop a business plan that covers at least 5 years, everything else seems to fall into place much easier, even things like a suitable business name or seller id in this case.
No great surprise of course, directions will usually get you to where you need to go a lot easier than trying to get there without them : )
The big thing to remember, when you are talking about sites such as ebay, people are searching for items, not by seller id's, so it's more important to focus on actually branding each item, to that of building a business brand for yourself.