Hy Dwarahkesh,
this depends on the default unit of measeure for sales order.
If default Sales UoM = Eaches. Sals price will be searched with for this unit. Base price, trade agreement, … should be setup for eches.
If you then change on sales order line the UoM to Carton, and a Unit Conversation is setup, it will calculate the sales price in the moment you change the UoM.
If the default Sales UoM = Carton, price for carton will be searched, means that also base price or trade agreement price should be setup with UoM carton.
If you change UoM to each at sales line, it will be calculated as Setup in uoM conversion.
You also can setup both prices for eaches and carton in trade agreement with to journal lines.