Assigning inventory to a customer

Does anyone have a best practice for assigning inventory to specific customers? Here is an example of what we are trying to do and examples of what we are doing at the moment (but looking for a better method).

Example/Goal: bring in inventory and allocate/assign it to specific customers. Serialized Inventory Items would need to be assigned per serial number per customer, standard Inventory Items would need to be assigned to customers based on quantity.

We inventory an exact same model tablet for multiple customers – could be something like 100 for customer A, 500 for customer B and 50 for customer C. We need to be able to see what inventory is available for each customer so as they submit order for us to fulfill against their inventory, our warehouse team knows which product to pull from which customer inventory location.

How we’re doing it today: using warehouse locations to determine if it’s our owned inventory or customer owned inventory. Assigning or earmarking inventory for customers based on an additional “customer” field we added to the Bin Number. We’re also looking at possibly doing unique item numbers per customer, but this isn’t scalable as the quantity of item numbers will continuously increase and become difficult to manage.