Hi,
I too have come across this and in the end I had to just write it off and put it down to experience. It has made me rethink how I deal with payments. I now ask for payment up front. Even if it is only one week at a time. The payment is made and then they come for their session.
Up to now everything is working as it should and providing you have sensible conversations with your students, I think that you will find most of them will be agreeable.
I hope this helps.
Cheers
Bill