When an item is listed with the Best Offer feature, the seller can specify a Best Offer auto-accept and/or auto-decline price.
Use GetCategoryFeatures to determine if these features for Best Offer are supported for the category you want to use. You'll want to include BestOfferAutoAcceptEnabled and BestOfferAutoDeclineEnabled as FeatureID values in the GetCategoryFeatures call request.
If you set a minimum Best Offer price and a Best offer does not meet it, the Best Offer is automatically declined. If subscribed to the corresponding platform notification, the buyer will receive a BestOfferDeclined notification. The minimum Best Offer price is specified through the Item.ListingDetails.MinimumBestOfferPrice field of an Add/Revise/Relist/Verify call. A minimum Best Offer price can only be specified for items listed in categories that support auto-decline for Best Offers. If a minimum Best Offer price have been specified for a listing in a category that supports auto-decline for Best Offers, GetItem and GetSellerList will return the Item.ListingDetails.MinimumBestOfferPrice field.
The auto-accept price is the price at which Best Offers are automatically accepted. Specify an auto-accept price through the Item.ListingDetails.BestOfferAutoAcceptPrice field of an Add/Revise/Relist/Verify call. The first Best Offer that meets or exceeds this value will automatically be accepted.