This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development is uncertain. The modern form combines 革 (leather) with 賣 (sell), but the original semantic and phonetic roles are unclear.
The left side is leather 革, and the right side looks like selling 賣. Imagine a leather goods seller, but the true meaning is uncertain.
For トク, imagine a leather merchant named Toku selling his wares: Toku -> トク.