Seller Details is a composite of the 5 different section tags: [SHIPPING][PAYMENT][TERMS_OF_SALE][ABOUT_ME][CONTACT_US]
You used the word "apply", which I'm guessing means you are trying to apply a Profile for sellers details to a listing. A Profile for Sellers Details can have each of those 5 sections and its selection on the one-page lister applies all 5 at the same time (if you have the 5 tags available on the template, and Auctiva's ready-made have all 5).
Sellers Details can be added to a Master Profile only by the the use of an Item Details Profile (which has the ability to fix/apply a specific Template and a corresponding selection of Seller Details). I believe that's necessary because Seller Details can only be used in combination with a Template, and Template is only available with the Item Details Profile.
Danno