When you show someone an opportunity and they have went through all the pre-qualifications by you, looked at all the websites, 3 way calls with your upline, educational materials, conference calls, gotten all of their questions answered and their concerns addressed. I think when you do it properly and go through all of those steps then you really shouldn't have to try and sell them on anything.
People can tell when you are trying to "sell" them something and human nature is that no one wants to be sold on anything. People want to make up their own minds and sell themselves. They have to make their own decision without any pushing from you. I think when you have to push a prospect into making a decision then you will always have to push them to work on their business. There really isn't a steadfast rule though as Adil pointed out...this is something you have to read in the prospect as to when you should ask the closing question. Note: closing question...not a high pressure sales pitch. We are in the telling business...not the selling business.