I post my rates because I personally don’t like having to contact someone (usually a salesperson) to find out how much something is going to cost. My rates are what they are and not posting them isn’t going to change anything. Surprisingly, only about half of the people that contact me through my website have looked at the rates when then contact me. For what I do (mostly working with people who have exhausted their rehab benefit and high end athletes), my prices are low (high compared to the area Personal Trainer average).
Posting your rates gives you the platform to discuss cost with clients. This is often a difficult topic for many fitness professionals. Having your rates posted makes this less of a challenge. When the topic comes up or when you must bring up the topic, you simply bring up your website (this will also help you market your services as you can suggest that the client direct people to your site at this time) and go over the rates you have on the site.