Earlier quoted context omitted.
I've bought fake followers before. It's actually fun. You'd be surprised how much of the "chattering class" will check your follower count before they decide if they should read and respond to your comments. If you enjoy chiming in on national conversations then it's a cheap way to appear prestigious. Of course, you need to be able to argue well enough to not out yourself as some random joe.
I wonder what proportion of the chattering class will pay attention to measures of retweet:follower ratios. It's a good proxy for a fake account.
A look at the history or content of mentions is probably the best bet to detect a faked account. Still, a clever person might slip by a cursory check.