Question: I often have to hail a taxicab on a busy city street and once, while in a big rush, did so by signaling with an upraised hand to a driver headed in the opposite direction. He nodded his head in acknowledgment of my signal and began to circle around to pick me up. Another cabbie who observed this scene and was hungry for business pulled up to offer his services. Accepting his offer would perhaps have saved me a minute of waiting for the first cab and I was in a hurry. Whats the right thing to do?
Answer: A cabbie once told me that taxi drivers have a special name for one of their own who tries to steal another drivers business but it is hardly worth repeating in such a dignified publication.
In regard to the legal and moral obligations when one enters into a transaction with another and then wishes to back out there are distinctions made in halacha. A formal kinyan grants the other party the right of legal enforcement, while only paying money in certain cases or merely giving a word in most cases raises only the moral question of faithfulness.
When you hail a taxi it is a virtual promise to that cabbie that you are hiring his services and there is a moral obligation to remain faithful to that promise. Similar situations arise when people making a wedding make promises to a photographer or a band and then wish to back out and we can probably list dozens of other examples.
In our morning prayers we say that a man should be "G-d-fearing in public and in private and speak truth in his heart". The paragon of this last attribute, says the Talmud, was the Sage Rabbi Safra. He was once in the midst of reciting the Shema when a customer came to make a purchase. Since he could not interrupt his recital to acknowledge the buyers first bid it was interpreted as a rejection of that bid and a higher offer was made. When Rabbi Safra concluded his prayers he insisted that the buyer pay only the lower bid because in his heart he had acquiesced to it.
If one must be true to his thoughts how much more so must he be true to his signal and word.