How do you ensure that the money doesn't disappear during the transfer?

Threats won't get you anywhere, you'll need to put these items in very kind terms or save them if the association gets nasty with you.

I've gotten e-mails correcting my Post, threats to take down my Post if they violated Rules etc.  

Or does this become a hassle, as a lot of the students could disappear for the summer, and leave you hanging?

9 times out of 10 threatening court action is just that , a threat.

I'm glad I did because the money would have disappeared into something else.Frank

If that threat doesn't get them to pay up, you should evaluate for yourself the time/effort/cost of a lawsuit and the probability that even if you win they will pay up. 

The longer your tree hangs over the fence, threatening your neighbour's house, the greater the risk to you (you will be liable for damages if you do not take timely action to remove the tree (threat)).In the end, your insurer will re-imburse you the agreed amount minus your deductible.  

What if you could make that stress disappear?...

I know there is the 'due on sale' clause that could be a possible threat here so what is the solution?