I get the distinct impression that no matter what words I could use to define these terms you would simply ask me to define those words in turn and then the words I use to define them, and so on in an infinite regression that would get neither of us anywhere.
Straightforwardness is simply being what you say you are and doing what you say you will do. I realize, of course, that most, if not all of us, come somewhat short of that ideal from time to time, but there can't be any reasonable doubt that it is a worthy ideal -- not in my mind, anyway. If you don't think so, I hope I will never have the misfortune of meeting and having to deal with you in person.
As an example of unfairness, suppose I contract with you to provide a product or a service in exchange for something from you and then refuse to provide what I promised after getting from you what I wanted. Would you accept that as valid example of unfairness? Or how about if someone faked an injury on your property in order to sue you for everything he could get from you, would you regard that as unfair? I could easily come up with many examples of conduct that would satisfy any reasonable person's criterion for unfairness or dishonesty. I imagine your only response to that would be to demand that I define reasonable, and then to define any conceivable word I could possibly come up with to try to satisfy that demand.