PR is completely meaningless to probably 90% or more of people out there. Most have no idea how it is calculated, what it means, how much it is weighted in actual SERp ranking etc. (and this includes the majority of people pushing PR as a sales benefit.) I'd say ignore that and look at what you are doing to demonstrate the value of the domains? No buyer cares what your opinion is. How does the domain actually stack up in terms of search volume, AdWords daily cost for the term, character length, TLD, pronounceability, memorability etc. in the context of being compared to what they have now?
Also, how are you finding your prospects? The fact that you get responses at all suggests that you may be getting some decent prospects, but if you're pitching mainly other domainers (who will tend to jump right to price) you're wasting your time.
Frank