Pay is highly variable, they like to lowball newcomers, especially with light/no experience. It does seem that CP is one of those places where you need to establish yourself for a while, leave, and come back to get the good pay.
The commission plan is INCREDIBLY complex and will take you years to understand, if ever. This is not exaggeration. It is my opinion that the only reason to make it so complex is to make it difficult to make your numbers or obfuscate some things. You cannot reliably predict the commission and you sometimes get behind or ahead and end up owing them money. Also, the quota is very very difficult to reach. I would estimate only about 1/3rd of people make their quota in any given year.
CP also is a tough sell. It is expensive comparatively. And it suffers from some staleness, not so much on their products but on their marketing and general sales gameplan. The competition is fierce and they are eating CP's lunch pretty regularly. And again, it is not really an issue with the technology or the security effectiveness.
There's also a little bit of a hard time figuring out "what's the next step" for someone who wants to climb the ladder.