I really like this definition of reputation by Seth Godin:
Reputation is what people expect us to do next. It’s their expectation of the quality and character of the next thing we produce or say or do.
We control our actions (even when it feels like we don’t) and our actions over time (especially when we think no one is looking) earn our reputation.
If you think about it, the businesses that you like to do business with are the ones that provide a consistent experience. You know what to expect, which makes it easier to spend your money with them because you know they will stand behind their product or service.