Yep, happens all the time.
I know the local organiser for all the Cancer Research events round here. All the race for life events around the county, mud races, relays, night events etc. I can't remember the exact figure, but is was surprisingly high the number of people that don't hand in their donations.
Then there was the lovely piece of work who took it a step further and spent a couple of months telling people she had cancer and needed to raise money for some pioneering treatment un the USA, then miraculously got better when people started to question her.