1 -- The customer or client who's reluctant to pull the trigger, wants to "think it over," or is indecisive.  If they leave your office without committing to the sale, chances are you've lost them for good. 

You can try to follow up with a phone call or even add an incentive like a discount... but it will be infinitely more difficult to get the sale if it's not made during the first meeting. It's not impossible, just much more difficult.

2 -- When you delay in asking for a review or testimonial. The longer you wait after you've completed the service for your customer, the less likely they are to give you a testimonial.

Here's a portion of an article from Entrepreneur Magazine:

"One of the most devastating missed opportunities I've witnessed far too many entrepreneurs suffer is the lack of testimonials, simply because they never thought to ask the customers. It is ten times harder to track down customers weeks or months later and reach them, let alone actually capture an enthusiastic, contagiously positive testimonial in comparison to doing so during a customer's current experience with your company.

One of the most strategic moves I made early on was to include a customer testimonial and feedback form that all clients have to fill out before the last piece of their service is delivered for one of my companies. In so doing, my team has garnered hundreds (maybe thousands) of detailed glowing testimonials without lifting a finger. These are in your own backyard if you act swiftly."