We have looked all over to find an answer .. where can we find an answer?
If they click on your ad multiple times, one after the other, it will count as just one click. If they click, then hit the back button & click again, it may count as another click that you pay for.
If they click & close their browser, or do another search & click your ad again, it will count as a new click (ie. you'll pay for both clicks).
Click fraud is a pain, but you do have to factor it into your PPC costs.
PPC fraud is a factor as pointed out above but it should be fairly easy to root out without overwhelming Google with spurious claims for refunds