That's overly general as by that logic nearly every action anyone takes is equivalent. Reliably show up for work? Self serving pursuit of a paycheck. Grocery shopping? Feeding oneself is also self serving.

Someone selling secrets (for example) I would generally assume to be motivated by pure greed coupled with a fairly blatant disregard for both criminal and financial risk.

In contrast, I understand affairs to commonly be motivated by any number of things ranging from lust, various relationship problems, the thrill of something taboo, etc. The risk is also typically more social than financial and certainly not criminal in nature (at least in the west).