In common commercial english, i would read that as “this merchant will offer to trade any of the books for an amoumt of currency equal to half the book’s cover price plus $1.”

Such vagueness also suggests sufficient informality that the merchant may either accept seperate offers or veto the general rule on a case-by-case basis.

Did you just intend to endorse organ harvesting and grave robbing?

And, if you want tax reform capital gains aren’t your target, but instead “unrealized gains”. A billionare pledging stock to back a loan should pay tax on their whole net worth’s increass in value first.