A few years ago we turned on PM's for Pro's only. PM's aren't allowed for guests due to the unreal amount of back door questions from HO's and DIY. If unwise advice is given in a PM then the site could be considered liable for damages.
There is no cost for going Pro here. It takes about a week to be converted after filling in the form and sending it to the Membership Committee. So, if you are in the business... fill in the form and go Pro.