This comes down to two key issues in sales: the obvious one is ABC. Always be closing. And if your sales people aren't closing deals then you get rid of them. The second is ABCD. Always be collecting data [1]. You need to collect data on sales constantly to evaluate productivity and have input into the process. It's simple if you follow those two steps.
[1] http://www.idealcandidate.com/always-be-collecting-data-the-...