Keeping one's word is persuasive because it provides consistency. If you're trying to decide how much credit a person's word has you look at your experiences with how often they keep their promises. Of course there are always exceptions that prove a rule such as if a commitment was made with faulty information or if the values of a party have shifted. When an extenuating circumstance arises communication and evidence based dialogues become a necessity in order to maintain consistency even when a promised action can't or won't be performed.

From a personal perspective I totally agree with kennyskitchen. Follow your gut even if it doesn't end up like you think everything will work out in the end.