Its a difficult furrow to plough, you need to reward them for effort, but put pressure on them when they lack it. You need to be very realistic with what you can expect from them. Why not benchmark the job for them by spending 2 days on the phones and see how many leads/sales you get. But be careful not to blitz it like a estate agent on speed, it needs to be realistic. Just an idea (it worked well for me in the past-on both sides of the coin)