How can we keep track of products that are ofered to the customer, but the SO is not fully confirmed?
Imagine a car workshop, a customer comes in with a broken car so we give them a quotation as follows (I'll ignore the money amount as it is not important for the example):
- 10 hours
- part A (2 uts)
- part B (1 ut)
- part C (2 uts)
Then the customer does accept the reparation, but does not want the part C (as it is not critical, or they might want to bring it to some other place to change that part, or they will do it themselves... whatever the case might be)
So I remove those lines from the quotation, and now whenever I want to check how many times was part C sold or quotated, it won't appear!
The same is true if I add it to optional products, whenever I confirm the quotation to a SO I'll loose this information.
Is there a standard way to achive that?

Why not change the quantity to 0 instead of removing the line?
I also thought about it, but:
1- It's dirty/confusing, then in the SO there are extra lines (not invoicable) and the customers might get confused.
2- Then I do retain the product, but not the quantities. This isn't as much of a hassle as the first point, but still...
If there is no better solution that might be the one, but I'm looking for some cleaner way.