Hmm, I think of "tire kicker" as someone who MAY buy, but will go over every little thing with a fine-tooth comb and then bitch and whine about each and every one like you, as the owner of the car, didn't know. They do this to try to get a lower price. Sometimes they will do things that are a little too "hands-on", things that would get them knocked out if it were my car.
On the other hand, if I see an ad that says "no tire kickers", I think "hmm, this guy has something to hide" or "this car has some problems and this guy wants a good price anyway". Interesting double standard huh?