A couple of years ago a local shop listed an EF 800mm, and whomever typed the price dropped one of the digits. Local law at the time was that companies had to sell products for whatever price they've advertised it, so I could have bought the lens for roughly 10% is price.
Damn, maybe I should have used the opportunity, rather than send a warning by email. They didn't even say thanks ...
[Since than local law was changed, saying if it's clear the price is in error, e.g. as in that case, the seller isn't obligated to honour the advertised price.]