In the retail business we have always the requirement that for a certain time, like a promotion, an item can be sold by a "net price" an no other existing discounts should be included.
At the moment we have to create additional discount journals for this item which makes certain that we get no discounts (line, multiline and total). We always have to program this function that it works in this way in the sale order line. As soon the price is flaged as net price then all other discounts are set to zero.

If we look a little further then we had also the requirement that you could select not only a sales price in the agremement as "net price", you could als select if one of the other discounts should be still active in the calculation. Example: item has a "net price" flaged in the trade agreement and we still want to apply the total discount. In this case in the sales price of the trade agreement the total discount flag was selected (so 3 additional flags for each discount type). In the sales order line the net price got taken and the total discount only. Of course this is a little bit a contradiction to the flag "net price" but we had this by a customer.