The seller name is the username of the mergant on tradebit.
You find the name on every product detail page. The name is below the
product picture and next to "Contact seller".
(left image is an example of the merchant "music")
In case you you are on a merchant subdomain, the seller name is visible in the URL,
between "http://" and "tradebit".
(right image show the subdomain of merchant "music")