Hi Daniel,
In Odoo there is a "Warning when selling this product" section under the Sales tab on Product form - need to activate it first through Settings. Where you can set to "Warning", so when your employee select the product and wants to confirm they need to double confirm. But, I guess this is not what you are looking for.
Extra addons I am not sure, sorry.
I do feel curious about the business flow that you are having now, maybe it's common just that I am not familiar because I am asking why are we not selling to customers? we don't want to gain revenue from certain customers?
Maybe you can share your thoughts on this.
Hope this helps.