Hello,
You can have more than 1 selling id. Infact some sellers have 4-5. But it makes sense only if you are offering different kind of products on different ids. It does not amke sense to offer the same products on the different ids.
Like if you are selling gems on this id and tomorrow if you want to sell electronics, you may think of having a different id (store), since gems and electronics would not have any synergy.
Or say a seller who has both lingerie and childerns books / vcds. He cannot obviously sell the same on one id and would need to separate id to sell the same.
It is more like the offline market where even though Pantaloon and Big Bazaar are owned by the same company and both are into retailling but have different identities and different stores.