Marshall asked: <<Is it really worth taking the time to help people who are not customers?>>
Yes -- with templates. It's easy to construct a generic response.
[Hi and thanks for visiting Blue Widgets!
We don't offer the products you need at this time.
We look forward to your next visit when you need the world's best selection of yellow flower beans (www.yfb dot com).
Good luck in your search!
The YFB Team]
I wouldn't run around and shop for the customer, but a template response that nice and cheery? That is rather easy to facilitate.