If you do not want the Customer.TradeDisc from being applied for orders placed from OrderCentral, this can be overwritten by setting the xctb_basket.DiscPct field to 0 for the line item or all line items.
Ex: UPDATE xctb_basket SET DiscPct = 0 WHERE sessionID = @sessionID AND basketID = @basketID
OR
Customize the xct_spAddCartItemWithPrice procedure to insert 0 in the xctb_basket.DiscPct field when the item is added to the cart.