When you say "seller" what are you referring to exactly? How do you identify "seller" for a sales order? There are fields for sales org, division, sales office, etc. I'm not aware of any standard fields called "seller", sorry.
Edit: to ensure a follow-up, please don't use Answer button but post a comment and use @ key to "mention" my name. Otherwise I won't be notified of a reply and might not see it.
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