When trying to quote a cabinet (with Reports -> quote), it always adds a 40$ charge called "base finished side".
It does not show up as an item in the item list, so I imagine it is a set charge added on to every quote I do.
I don't want this charge in the quote, is there a way for me to get rid of it?
Sounds like you may be using one of the SAMPLE-x catalogs.
In the Item List, it shows up in a separate column called Fin. Side and is indicated with L / R / or B. The only way that you can remove the charge is to go into the Attributes of those cabinets with a finished side and on the General tab change the finished side to None. Then the charges will disappear (but so will the texture in the renderings.) Someone with access to Catalog Tools could change the price of these automatic finished sides to zero.