Depends on how egregious it is and how frequently it happens.

In terms of egregious: Someone staying a few minutes over when they are in a store probably shouldn't be punished at all. On the other hand, someone parking in a handycap spot or leaving their car somewhere for a day or more should probably be a reasonably stiff penalty.

In terms of frequency: Perhaps start small but with an exponential increase for each time someone does it within a calendar year.