...or, if it walks like a duck. (With apologies to daffy )

Another thread made me think about just what sets off my "Quack Detector" and I had to conclude that a part of it is almost unconsious. It also seemed like a good thread since all of us are vulnerable to the little man with the bottles at one time or another. So, do you have a rule of thumb or two that makes you narrow your eyes and say, in your best Bugs Bunny voice, "Wait a minute...." ?

Here's a couple of mine-

1- Does it sound too good to be true?
2- Does it involve me giving someone my money?

Obviously it requires a preponderence of evidence but you gotta start somewhere.