Yesterday, I had to stop by the PO, so I thought, "Hey, why not get an unofficial FDC for the Frank Sinatra stamp?" So I grabbed a blank envelope, asked the clerk for a set of Ol' Blue Eyes (all is well so far), and then asked if she would mind giving me a hand cancellation (once I put a stamp on the envelope of course).
At this point, she gave me the "You are such an idiot," look. To sum up a somewhat embarassing conversation, she basically said the only way I could get a cancellation was if I sent the letter through the system.
I don't get it. I can mail this exact same stamped but unaddressed envelope to the USPS (with another SASE envelope to get it back to me), and they will give me an official first day cancellation for free. But the local post office isn't allowed to do the equivalent?

Am I really an idiot;
is there some legitimate reason for this? I would think the USPS would be happy to make a sale that was guaranteed they would never have to process. Or do I need to make another trip to the PO to talk to her supervisor (to promote proper education of the clerks)?
