I understand your frustration. It can be frustrationing when you really want something.
I have left messages with a large vanda grower, wanting to buy a certain plant. After 10 days I still have heard nothing. That same grower has done that same thing before. It really bugs me because I really want that plant and I know no one else has it.
Too me if you are going to advertise a product , have a webpage, email address etc and you are not available to the customer you should not advertise. If you has another job, I understand but you can even hire a kid/teenager to answer emails if you are away or busy.