There Are Certainly "Junk" Traffic Sources
Any ad vendor that tells you they are going to give you 1,000,000 visitors for $97 or something that is obviously being dishonest with you. Sure, his click counter may read "1,000,000" at the end of your ad run, but you've gotten no subscribers and no sales… Big Surprise!
Don't buy "Guaranteed Visitor", "Guaranteed Traffic" or "Guaranteed Signup" which appear to be ridiculously cheap. I've don't this a number of times and have never gotten any results.
There Are So Many Places To Get Traffic You Can Never Use Them All
There are far more legitimate sources for traffic than there are scam offers for visitors.
Here are some important points when it comes to getting decent traffic and converting it.