make dirty, become dirty
黷 centers on the act of soiling or staining something, making it dirty, or the state of becoming dirty. The idea is one of defilement or contamination.
黷 combines 黑 (black, dark) with 賣 (sell), likely functioning as a phono-semantic compound where 賣 contributes the sound and the idea of blackness relates to soiling or staining.
The left side 黑 (black) suggests darkness or filth, and the right side 賣 (sell) can be imagined as selling something that becomes tarnished or dirty in the process. Picture a black stain spreading as you handle a sold item.
For トク, imagine a toque (chef's hat) getting dirty while cooking: toque -> トク, and the black stain from the kitchen makes it dirty.