The key to successful business development isn't simply hearing the word "yes". It's hearing it fast. You need to know, quickly, whether someone you're in discussions with is serious about doing business, or whether they're not. If they're not, you need to move on.
As an example, I recently spent over two months in discussions with someone at Yahoo!, the Internet company, about a project. We must have had five meetings, and endless discussions, emails and so on about it. I finally decided to try to pin them down -- what were they planning to do? What kind of budget did they have?
The answer turned out to be nothing, and nothing. My entire investment of time and effort had been a waste of time -- time I could have spent doing something a lot more productive.
As early as possible, try to get some tangible evidence of whether or not the person you're talking with is serious about working with you (or someone). The best way to do this is to inquire about their budget -- either their personal authority, or the process of getting something approved, paid for and in process. If they can, and will, commit to putting some real money into the project, keep talking. If they can't, or won't, move on -- politely.