If you’re wondering what a tinker’s dam is, it is usually defined as something that is worthless. Some think that it was a curse as in a tinker’s damn which was considered of little significance because tinkers were always swearing; or it is a tinkers dam which is a small dam to hold solder made by tinkers when mending pans and once used, it is then of no value. www.phrases.org.uk/meanings/tinkers-damn.html
I lean towards the second tinker’s dam definition. Albeit, why would I say that the guarantee, for the Workplace Attitude Test (WAT), is worthless? The WAT test is designed to ensure that you don’t hire a person with a bad attitude in the workplace. Presumably, if you are asking for your money back you have hired a “turkey.” This puts you in a bit of a sticky wicket which is defined as a difficult situation.
(A wicket is the playing surface used in cricket. It is a direct allusion to the difficulty of playing on a wet and sticky pitch. www.phrases.org.uk/meanings/334550.html)
Overall, you’ve hired the wrong person and a few dollars back from us isn’t going to help you much. Fortunately, the Workplace Attitudes Test works well and no one has every asked for their money back.