There are a number of areas you can measure your sales people by. But one big measure is accountability. Do your sales people have a high level of accountability, to go along with a sense of responsibility?
Are they out in the field doing what you both know are their responsibilities as sales professionals? Do you have to chase them down for their activities? Do you have to continually prod and poke them to do what they are getting paid to do?
If you cannot think of a right answer to these questions, it is probably time to have a discussion with them. Also, keep in mind; if you care more for their success and careers than they do, then it may be time for them to find a different company that will fire up their passion about what they are doing.
In the end, little matters for the success of a sales rep except closing deals that make sense for both you and the client. But on the way you still need to measure what is happening in their career. And I would measure them to the level of accountability they claimed when you interviewed them and ultimately hired them on.
If they don’t measure up, you need to ask them the hard questions and make a decision on their future with your company.