The PPC suppliers are providing the service to us as an agency.
Although we are transparent with our clients about who we use and why, they trust us to deliver the best traffic, maximum ROI, best supplier for the job.
In most instances the supplier would have very little detail about our client and I'm aware of the suppliers contacting exisitng advertisers but not cold calling businesses.
You will never stop over-exuberant sales people, where I have a problem is where there is contradiction brought on by lack of understanding.
We've had instances where the supplier have been in a position to talk to clients (seminar, workshop etc.) and offered them things that we have not (content syndicated traffic, broad match traffic). That's not to say we haven't considered them, but it does then get questions asked that don't need to be asked.
We have often taken the search engines to see clients during the pitch process, but we try to protect the supplier from the client and the client from the supplier and generally that works well.