I've had a LONG run of possible buyers who exhibited every buying signal, knew my rates then dropped out just before the deal closed. Is it something in the air? It's never been like this before.
The absolute best thing you can do is get feedback from the people who are constantly bailing at the last minute. Without knowing why they are bailing you'll be basing any solutions to this problem on guesses - which is not likely to solve the problem.
There are so many reasons why this is happening, from poor prospecting to not listening/engaging in consultative selling.
Price is usually one of the last reasons people won't buy - especially if they already know the costs ahead of spending time speaking with you.
Find a way to get feedback. Ask directly, provide a feedback form, get mutual contacts to speak to them...just make sure you get their feedback.
Once you have a better idea of why you'll be able to adjust accordingly.