I tend to agree here but the problem may be also for the supply_on_sale checkbox.
I’ve seen some cases where the company supplies on sale but may also have some spare stock for the product (I didn’t have the time to properly understand why they have stock) so in this case the supply on sale is only required when there is no stock.
For most of the cases I’ve found, the supplier does drop shipment for all of it’s products, so most of the time having to set the drop_shipment boolean flag on product supplier produces produces more errors than benefits. So probably moving the flag to the supplier will simplify the usage a little bit.
Also the need of having proper delivery_dates set (the product_supplier is not picked for drop shipment if lead_times are not set) is something that probably should also be simplified.
I’m not sure about which will be the best solution, but probably having a selection method to determine the supply method (with a proper default for it) wil make easier to support more cases.