The law is a very blunt instrument. Not every legally viable claim should be pursued. Even if you have been in some way wronged by a business it may not make any sense to go to Court. Imagine you had a dreadful meal at a restaurant or you ordered a cab and it came a half hour late – in theory you might be able to sue for damages but so to do would be silly. The cost of suing would outweigh any recovery by a thousand fold and a judge could see your suit as merely a foolish waste of Court time.
So what can you do?
There are options.
One is to chalk it up to experience and forget about it. If you have choices you can not go back to the restaurant where you had a bad meal or you can use a different cab company next time but beyond that you can ignore the problem happened and move on.
The other option is to make a complaint.
Writing a complaint may get you some relief, change the way the business that harmed you carries on and, at the least, allows you to vent a little (but very little as we shall see).
So how to make a complaint?
It's best to make a complaint in writing. That gives you clarity and also allows you to say what you have to without interruption. People getting complaints in person often get defensive and things degenerate into an argument.
The complaint should be short, specific and very clear.
Begin by saying "I am writing to complaint about [whatever] that happened last [date and time as best you can say]". Explain exactly what happened – in the cab situation you could say "I had to wait over half an hour for the taxi to arrive". Then describe how this caused you a problem – it made you late for work or the bad meal spoiled the birthday event or whatever.
Finally, say what you want and ask for a reply within a fixed period of time – say ten days. What you ask for should be reasonable – say a refund of what you paid or some free service. If you ask for $500 because you cab was a bit late you won't get it. But if you ask for the next ride to two to be free you likely will get something.
You complaint should be polite and focus on the failing rather than the business. Don't send the complaint to people outside the business (local politicians and the like); the issue is between you and the business. Things go awry and the business likely didn't intend to cause you a problem. Focus on what went wrong and what you want and you will probably get a good reply.
Businesses take complaints seriously and they will respond to a polite and measured complaint in a positive way. And even if you don't get any compensation you will at least have the satisfaction of not taking this bad service lying down.