I've been ingrained with the "no such thing as a be back," but I have converted followups to sales. I've actually had customers call me back. This is my 2 cents: 1). If they give you the ol' "I'll think it over..." routine, you better try to pull objections out of them, they may very well be lurking and there will not be a follow up sale if you do not clear these out while you are presenting 2). Try like heck to close them while you are there, because the prospect is most definitely the greatest at that time, but not to the point of burning your bridge. 3). IMO, a product that offers real value will still have appeal even after the customer has "slept" on it, if they liked you, believed you, and saw benefits to them.
I will follow up with prospects who didn't buy if I feel they seemed like a strong candidate, but I consider these sales are bonuses, because I write them off in my mind, if they did not buy the first time around.