Hi,
Buy shipments will always be built in your parent domain (even if you have a 5 deep child domain structure).
Look at this to understand:
- Each customer is a child domain of logistics company which is the parent domain.
As a logistic company you want to have savings by combining several customers in an equipment. Then it is mandatory to have it in one shipment. For that shipment you have to hire a carrier (buy) to do the job. Because it needs to be in one shipment it is the reason why buy-shipments are always built in the parent domain.
With all this saving in transportation you also need to send a bill to your customer for getting paid something (mandatory to survive in transport

). You don't want to have the customers to have also visibility to orders from another customer. Because you want to build seperate shipments from the orders on the customer side to get something paid (you
sell something), you need to consolidate a bit different. For the consolidation and visibility the sell shipment is always built in the customer (child) domain.
It is not always neccesary to have another itinerary for this sell side. You can set an ititnerary to be used for buy, sell or both. An itinerary is not child-domain specific as I recognised.
If this still doesn't give any clarity please ask again.