| | First of all...
When talking to those clerks, actually find one that has one of yours on his/her belt. Ask them how long they have been using it. Anything less than a month, move on.
As for your immediate problem. Go to your Profiles and then actually CHECK the settings for the Vibrate mode. Just selecting it doesn't necessarily mean that it's set to vibrate. On the 8310, you have to go to Advanced under Profiles to actually change the settings. It's pretty self-exdplanatory after that.