I'd like to know if there is a more 'correct' approach for this problem.

The problem:

Given a company x, x will transfer a quantity of a product to my company, let's say 1000 jeans. I create a transfer from the client WH to my company's WH, since no purchase is done. after this the 1000 jeans are let's say washed in 1 day. The client is charged for the service 'washing', then the products are transferred to the client location when done.

What am doing for now is creating a purchase order of the 1000 jeans with 0 as a price and when the washing is done, I sell the 1000 jeans with the price of the service 'washing'.

This is of course temporary, I want to know if there is another approach to this problem.