People tend to play tighter live because they're less likely to be bored and because they're more aware of the money (I'm sure there are other reasons). Since the most common mistake in lower buy-in events is to play way too loosely, this makes live games tougher at low buy-ins.

However, at live games, it's way easier to pick out the donks quickly because usually they'll announce it by saying "you can't win if you fold" or something dumb like that.