This answer is a bit out-of-universe, but bear with me. Qui Gon Jinn operates under so called "good smuggler morality". Typical representative of this morality would be Han Solo, but many more protagonists often display such behavior including Jinn's student Kenobi, Luke Skywalker, Ezra Bridger, princess Leia and even Yoda.
It is recurring theme in SW universe that Force is grey, i.e. there is good and bad in everyone (or almost everyone) . As Force is grey, so is the world it creates. Main characters must remove themselves from "dogmatic, narrow view" of good and bad. During their adventures they often encounter various creatures like Watto, which at first look are really disgusting (greedy slaveowner), but at second look are not all that bad. And, with some persuasion, even such imperfect creatures could be used for good without destroying them or robbing them.
Therefore, good smuggler morality (and Force) allows our hero to bend rules somewhat when dealing with creatures like Watto. After all, it is expected that Watto would on his part try to bend rules in his favor. But outright thievery or murder is not allowed, because this would actually have opposite effect of increasing evil in the world (strengthening Dark Side) . In fact "good smuggler morality" implies reciprocity : be good towards good, you could be gray towards gray like Watto, and you are allowed to kill evil (Empire, Separatists etc ...)