This is a new category–questions people are asking.
Question: Would you buy a young horse that clicks when it walks?
My assumption is that the question is joint clicking–not forging, which is when the hind foot strikes the forward heel which for whatever reason has not gotten out of the way in time–that makes a clicking sound too.
I have asked around in the past about the actual reason for joint clicking, as many of them do it. No one I have talked to seems to know exactly what causes clicking, but if new news is out, please pipe up!
Answer: given we do not know exactly what causes joint clicking–usually in the hind fetlocks–it is not a 100% deal breaker for me. But I would certainly prefer they not do it. First, though it quite possibly is ligament noise, it makes me nervous about wear and tear. Second, I associate it with stiff horses–not lame ones, but tight ones. You rarely see a loose, fluid mover with this noise. That said there is nothing wrong with working tight, strong and somewhat stiff horses–they can be good too–you just approach them differently. Also, interestingly, clicking can come and go. Some horses do it when young and then you notice that you are no longer noticing it. . .
If we are referring to forging it is typically a sign that the horse is on the forehand–retarding the flight of the front foot, allowing the back to strike it. Lots of green horses do it and as they get more balanced it goes away.