There is no harm trying out different instructors. Note that instructors have different strengths. Some may be better at teaching tailwheel and others at instruments.
One problem is that you will not really be able to tell the difference between a good instructor and a better one in one flight, unless it is a personality issue. From a technical point of view it will be hard to tell.
Better instructors tend to get booked up and are hard to schedule. If your instructor's schedule looks really full, that is a good sign he is a good one. Also, look at their flying experience. I notice that the better instructors tend to have more flight hours.
Once you start flying be sure to get "check rides" from other instructors once in a while. Different instructors have completely different styles and areas of emphasis, so it can be very useful to get "alternative points of view" from time to time. A new instructor will usually teach you new stuff. In this sense, even a bad instructor can be good sometimes because they can teach things maybe your usual instructor does not know.
Beware of "easy" instructors that just soft shoe everything. They are the nicest instructors, but they are slow teachers and they can be derelict and just "go with the flow" when they should be correcting you. If one or two instructors tell you that you should not fly and are not cut out to be a pilot, the dumbest thing you can do is to find an easy instructor who will just collect your money, even though he knows you are not pilot material.