It discredits catalog publishers as much as it makes the hobby seem fishy and should not be a secret. It is reality. They should not set a valued minimum and try to judge how a seller would price an item for common material. There are sellers like Mystic that price above catalog. A better approach is like some coin books did where they list a buy and sell price.
I do buy modern material off
ebay and usually end up nearing paying face for small quantities since I want a specific item (plate number, etc). I do not feel like I am being taken since I just use the stamps at any time.
In fact with one seller, I purchased a booklet at face and the seller used the same stamps on the mailier - that was intentional.
Al