Out of curiosity, that I am missing?
I think if you report them (in messages etc.) you are also no longer able to see their profile so this might be a solution?
There are posts on the forum that if you report someone through the messaging system (unless the end up getting banned), it’s only a temporary communication block. They can still order.
It’s possible something new has happened in the past few weeks, but if not, there is no way to block a buyer.