Has he or she paid you for the item/items ? Or in other words: Does that person owe you money ?
If yes, I would give him or her a last chance and if you don't get an answer sell everything and try to get your money back.
If that person already paid for the items, I would wait a little longer. I mean, in the
worst case you got some stuff for free.
But remember that it is possible that the person could have some serious issues to deal with first. As nice as collecting cool stuff can be, there are more important things in life.