Simple- Staying in touch with them. 

I dont do anything.  I am not a used car salesperson.  If they can't decide for themselves, they are not ready to purchase and should not until they are ready.   I will "talk" a client out of a property (which I do a lot) before I ever "talk" them into it. 

I ask what is holding them back from making a decision. If it is about getting more information I want to do that.

Winston Heverly There could be a multitude of reasons why they won't get off the fence. Ultimately, it is their decision and no matter what you say isn't going to make a difference. John McCormack summed it up nicely.

Finding an opening in the fence. Sometimes you fall off the fence but its easier if you find an opening and walk on through to the otherside.

You can talk and talk and talk and tell them they love it, prices are rising, bla bla bla and they will still do what they want because of other issues that they have not shared with you.

At the time they identify 'the' place I reveal to them that my preferred lender and I collaborate to create a down payment assistance plan that is in effect until the end of the month. This is in addition to any other incentives that may be in place AND allowed.

If they decline this opportunity, they are moved to the B list. Their level of commitment has not reached the necessary urgency.