That said, I still visit professional shops rather more than I should (it depends on the shop.)
Of course charity shops are cheaper, that's part of the appeal, but I have more success in them because they are less discerning.
Over the years I've acquired a LOT of books, so now I tend to limit myself more. Mostly I now collect science fiction, with an emphasis on work pre 1970. These were made cheap, and are usually in "poor" condition now.
Professional shops won't shelve them, whereas charity shops will, so I have more success there.