This type of business works in the small - when you know your suppliers and your customers. It doesn't work if you have 10,000 customers, or if anyone can email you. For this business it's only a spam problem, though - they have to reject emails from strangers if they get a high volume, exactly the same way they have to reject emails selling Viagra.

That's probably alien to HN and a lot of them may try to contact him, as if they have a possibility of becoming his customer, which they don't.