Just find an instructor who has multiple students. Ask the students what the instructor is like. The best opinion of a teacher comes straight from the student. That's how I found my first instructor and he's got a real talent for teaching (as well as piping). I'd recommend him, but he is currently in the service and not available to teach.

You can also go to pipe bands and ask if there's anyone they could recommend. Typically, there is a couple pipers in every band that will take on students (without charging much for lessons) for the sole purpose of recruiting new pipers for their band.

You get the lessons cheap as well as a foot in the door with an established pipe band. They get another piper (which are fairly few and far between). EVERYBODY wins.