Unfortunately, there are some bad apples among your buyers. But how would you know? You can set your Buyer Requirements to minimise the risk.
Buyer Requirements allow you to set a list of criteria that reduces your risk of running into problematic transactions.
Your criteria will automatically filter the buyers who can see and purchase from you. For example:
eBay.com > Hover over the top left corner > Account Settings > Site Preferences > Buyer Requirements > Edit
You can also filter buyers by the country they come from. This is prudent for countries where the postal system is not reliable or a country which is currently facing unrest.