If you are a store own, AND
1. People repeatedly coming in to your shop asking to buy something, AND
2. It is similar to the kinds of things you sell, from the suppliers you usually get supplies from, AND
3. You don't sell it
Then it sounds like your neighbour the notorious liar is doing profitable marketing for your business and sending you leads which you could profitably sell to, if you sold the item.
If there's a single customer who arrives via hallucination, ignore it. If there's a stream of them, why would you not serve them if you can profit by doing so?
There are obviously instances you'd ignore and you seem to be focussing on those rather than what OP was obviously talking about, repeat instances of sensible ideas