I just started AdWords. I put an ad and it said all my keywords, although most were fairly obscure, needed a very high bid. I actually put that bid in, since I am only experimenting here. So that seemed to work, (most of) the keywords stopped being "Invalid for search" or whatever it says. But now I log in and see that a bunch of the keywords have gone back to invalid! Investigating, I found that my max CPC had somehow gone way down. Well shit Google, no wonder they are invalid! If you'd'a stuck with what you made me type in like 6 times in the first place, we'd both be happier. What the hell is this? And more importantly, whatever it is, is this really the best way to do things? All automated, overfull of algorithms, and completely mystifying without hours of intense study of their zigzag, secret logic?
If your CTR (click through rate) and QS (quality score) are not good enough google will charge you more money per click.
Well, despite my research I'm still vague on the QS concept. But aside from that, why would it jump way up and down within an hour or two?!? First it was no good, then it was ok, now it's no good again.
mad4 is correct it depends on your keyword relevancy and CTR . if u improve your CTR your Max CPC automatically short down. So try to optimize the keyword and CTR.
I highly doubt Google is accessing your account and lowering your Max CPC. That doesn't make sense on a number of levels.