In some cultures, e.g. in East Asia, South America and the Middle East, people tend to avoid saying no to requests.
They also intend to keep their promises (which are different in nature from e.g. a European or US promise), but as it sometimes turns out, they are unable to do so.
Try to live in e.g. Thailand, where people "even" smile, when they regret to have failed their promise, it's a culture thing.
You simply have to learn this and also slowly - guided by experience, yours and other's - hand pick the people who have the Western approch so they at least inform you that they are unable to fulfill their promise.