Some of my best ones are:
"I know nothing about cameras"
Roughly translated, I know this one doesn't work, but if I say so, I'll get nothing for it!
"In mint condition"
My mint is your rough, but tough, I'm not an expert!
Rare
Actually quite common, but I think its rare and another fool will be along in a minute!
(eg last week I was amazed to find a 1939 Camera Dealers Catalogue fetched £23, since I acquired the same catalogue the next day for £3!)
Collectors Condition
Really quite awful, but you collectors will buy almost anything.
I could go on............