For example, clients who insist on using amateurs (sometimes themselves) to create a logo rather than hiring professionals?
In order for them to see your point of view, you first have to understand where they are coming from and what the core issues are. Starting asking them questions that make them think and ultimately guide them to a place where they will begin to see values. Listening is a great sales tool.
If you have case studies with real ROI to prove your point, then that is even better.