I completely agree with keeping promises. I have been freelancing for over 2 years and have also hired freelancers. One of the first rules I set myself was to always deliver something by the due date.

There have been times when I have hired freelancers and they message me the day before a project is due with some random excuse as to why they need longer. I agree to their extension but I can guarantee that I will never hire them again, even if the work is good. I am certain that other employers feel that way too. It’s not worth the risk of damaging your reputation, especially if you are freelancing where people can leave reviews on a profile.