Feeback from fellow professionals is a must. Go get em'
I also think that we all need to remember to give that feedback when asked - it's easy to ignore, but we all need it!
I call the showing agent shortly after scheduled showing or when notified of showing access.
Because of the difficulty of completing many of the on-line feed back requests via email I do not respond to any of them. Nor would I fax a form. But I do answer my phone. So far I have found this method not only allows be to verify who the potential buyer is but also 100% of agents will give feedback via telephone.