hi mike…
Qualifications do work :). but of course, not all the time, as it depends on the area you want to qualify, on the state of the picture (codec, exposure etc.) and on you’re approach of keying.
generally i ask myself: what did you try already? you can get rid of the flickering-issue by blurring the key. this should be the last step, because if you blur too much, you will see the soft “edges” of your qualification. try before to soften the H S and L. try the new clean black and clean white parameters etc.
you should also bear in mind that for a succesful key a balanced, kind of neutral picture helps a lot. if your whole picture has a green cast and you are trying to key out a green jacket, you might get in trouble. if your picture in general is very warm, you might get into trouble qualifying skin tones etc. try to key from a balanced picture and add the style after the keying.
if you are still experiencing flickering, you could also try to denoise the picture before.
and the list goes on and on and on…