You invited your family to have a special celebrate dinner in a well-known restaurant, but you are unsatisfied with the meal. You are writing to make a complaint. In your letter, you have to say: What the situation is; What the problem is; What you want them to do.
Dear Sir,
On October 20th, I took my family members to your restaurant to celebrate my mother’s birthday. My friend recommended your restaurant as he is your regular customer. However, my experience has not been so good.
My first complaint is that your servings are too small and not at all value-for-money. We ordered your giant burgers thinking that one would be enough for each of us. But your giant burger turned out to be just the regular size that we get elsewhere. Then, when we asked for extra sauces, your waiters told us that we would have to pay extra. They were quite discourteous also.
I think that it would be a good idea to either change the amount of food you serve or reduce the cost of the meals because at the moment I think your prices are too high for the amount of food you serve. The extra sauces also should be free with the food ordered. It would also be a good idea to teach some basic manners to your waiters.
I would like to be your regular customer for the quality of food you offer. So, if you look into the other things it would be very nice of you.
Yours faithfully,
Kiran Makkar
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http://kiransielts.blogspot.com/2011/06/ielts-letter-you-invited-your-family-to.html#more
Correction:
"a special celebrate dinner"
should be
"a special celebration dinner"