Business Tip: If you say you are going to do something,

DO it! Your integrity will make or break your business and if you cannot be trusted, it would be better for someone to have never worked with you. Even if you do good work, if you do not hold yourself accountable for what you say, you will be out of business.

If you absolutely cannot, then have a detailed answer of why it cannot be done that way and what the solution is that you have proposed, and you initiate the conversation to the person it most directly affects so they are aware of the issue and their integrity is not in question. This is some of the best advice I can offer being and entrepeneur.