Thanks for coming back and sharing the details of your concern, @MRK9.

In order to effectively manage inventory, it's important to have a good understanding of how QuickBooks deals with inventory assets, average cost, and Cost of Goods Sold (COGS). This article will guide you through the process of calculating the average cost and help you identify which report will be most useful for inventory management:

Understand inventory assets and cost of goods sold tracking

Inventory adjustment is the process of changing the quantity or rate of an item. It includes any increase or decrease in product quantity that is not due to a sale or purchase. 

Indeed, if you don't want to increase the sales for the in-house inventory you can create a separate item for this in QuickBooks Desktop. Then a separate item for those you bill to the client.

Note that it’s best to reach out to your accountant for advice before you adjust inventory value. 

Moreover, I'll be sharing this article to help you in your future work in QuickBooks Desktop:

Add, edit, and delete items in QuickBooks Desktop

How to set up inventory in QuickBooks Desktop

Feel free to reach out with other questions or concerns about Inventory in QuickBooks Desktop. I'll be glad to assist. Keep Safe!