IMHO, lots of persons in business, I'm talking about the little "Mom 'N Pop" operations, do not view cheating and nefarious practices in the same light as the rest of us. My personal experience has been that in counting my change, if an error is made, 90% or better of the time it will be in favor of the vendor. In situations where the register figures out the change, a non-existent item will be entered.
In many restaurants, the fine print on the menu tells you that the gratuity will be added to the check. Still the waitress will encourage you to leave something on the table.
Good Advice: In situations where taking the advice of someone will put money in his pocket, DONT ! !
At gun shows, I find that I can get a better deal if I deal with a woman. It is easy to see that they are often unhappy, and could think of a thousand other places that they would rather be.