There are two things which cost an inexperienced Sales Professional a lot of money. I should say a lot of time and money. Simply said, it can be boiled down to "Knowing When to Stop & Knowing When to Keep Going". It's all too common for a prospect to end a call or a meeting with a hint of hope for doing business when in actuality, there is no intention or no budget to do so. Usually a seemingly innocent statement with no malice intended, the most common one being "Send me the literature". Many people find it quite difficult to tell you something like "We are going to pass on this one", or "We have decided against it" or even "This is not going to happen".
That being said, it commonly understood that 80% of sales happen only after the 5th follow-up. You would not believe how many sales get started, but left unfinished. I personally ran into several situations where a prospect would tell me that they had seen what I was selling, wanted it, but the rep who brought it to their attention was no where to be found. They had no recollection of the rep's name and no way to get in touch.
So, how do you know when its time to say "Next!" and move on? How do you know when to keep going? Based on the above, you cannot tell by what they say. It's more about what they are willing to do. Will they discuss their need with you? Will they provide you the details on the problem your product can solve? Will they tell you who all the decision makers are? Will they introduce you to the other decision makers? Are they willing to discuss timelines and budgets? The worst thing they can do is tell you early in process "Send me a quote or a proposal". At least if they just ask for literature, you can do that in a few minutes. Sometimes a proposal can take hours to do. I cant tell you how many hours I would like to get back from time spent on proposals from my early days, where the prospect never had the money. I had no idea, that this deal not only wasn't going to happen, but it wasn't even possible. Your first clue: You are working on a proposal and find you have too many questions you need to ask your prospect before you can finish the proposal.