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.
Well, this happens during certain periods with almost every sales person I guess. :) Here is what I'd do (and I do as well) -
1. Send them an email, politely wishing them best, and asking to chose the reason they didn't chose you; give them options like - a) price was super high b) wasn't happy with communication so and so forth. I get a reply almost always to such emails if the buyer is genuine.
Also, you may lately find that most of them were not looking to purchase at all, so don't bother much either.
2. Check the competitive rates, figure out what others are charging for the same work. Need I tell you the ways to do that? :)
3. Just general review your in-sales process (where you send agreements to sign, deal closing documents etc) or probably do a role playing putting yourself in customer's place, and ask you colleague to play you. It sounds interesting, and it works equally good.
At Agicent (my company - https://www.agicent.com), we sell app and web development services, and we always role play to figure out what "Category" of customer would search for which keywords, and then we divide those keywords according to role and work on them (for content, marketing, pitch etc).
Hope this helps.