Those testers are but aids - and no substitute for either training, or a real meter.
A number of things will lead to confusing readings; among them are multiple faults and broken receptacles.
What you should do when you get multiple readings, or nonsense results, is to kill the power and remove the receptacle from its' box. Then you can start checking things.
Often these problems can be traced to one spot. I find it easier to locate the problem by first checking ALL 4receptacles. Ones that indicate problems get a piece of red tape on the faceplate; when I'm done, it's often possible to see a pattern. For example, they may all be on the same circuit.
