Complaining to a Shop or Restaurant by Letter

Occasionally we have all been in the situation where we have bought something from a shop or had a meal in a restaurant only to subsequently find that what we purchased didn’t live up to our expectations.
In most cases, this can easily be resolved. If you’ve bought something from a shop and found the goods to be faulty, damaged or not as described when you bought them, you can simply take or send them back to the store and they will either replace them or offer you a full refund. Likewise, if you go to a restaurant and your meal wasn’t what you ordered or there is something wrong with it, you simply call for the waiter who will replace the meal or offer you a refund.
However, there are some occasions where disagreements might ensue and you might need to put your complaint in writing.