More importantly - why even worry about it - you cant measure it - unless you truly believe the toolbar gives a real indication of PR but then you would just be following what most have come to believe is gospel. I do trades everyday with sites that have no "indicated PR on the toolbar" dependent completely on what the WM is trying to accomplis and how they are doing it - and its worked great for the 5 years Ive been playing in Google
One thing I learned a long time ago - if someone sends a trade request and they start by saying "my Pr is..." I trash the request immediately