We recently signed on for "Call Display" service. It is wonderful - if the number is an "Unknown Number", we let the answering machine take it - 99% don't bother to leave a message.
EDIT: And on the subject of the thread ...
I recently saw a box on display in a camera store that at least purportedly contained a new lens I might be interested in. I wanted to see it "in the flesh", but they declined to open the box for me unless I was willing to state that I was actually in the market to buy one.
I don't know if that store had a policy to automatically give a discount if a lens had previously been used for "display" purposes.
The lens in question wasn't a particularly rare one.