will eBay block him, give him selling restrictions even a complete ban from selling, if buyers open enough cases for item not received.
I take it the only way you know this is a ' habitual event', is because the buyers are leaving that feedback of non receipt of items? Otherwise, how do you know?
Feedback is good it warns / shows prospective buyers the type oof seller they will be dealing with, but unless they also open cases, eBay do not look at feedback, they deal with many that are left in error, some are left trashing a seller's account being a competitor, so its not a perfect guide
If too many cases for item not received are open, this would raise red flags to eBay and they then act with sanctions and bans.
@panpaper