The customer is unhappy. He would be a complaint about this situation

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1

The customer is unhappy. He would be a complaint about this situation.

2

The customer is unhappy. (correct English)
He would be a complaint about this situation. (incorrect English)
The customer is unhappy. He will make a complaint about this situation. (correct English)
The customer is unhappy. He will file a complaint about this situation. (correct English)
The customer is unhappy. He will submit a complaint about this situation. (correct English)
The customer is unhappy. He will complain about this situation. (correct English)

These verbs are called “modal verbs” : shall, should, can, could, may, might, must, will, would
All of them, but “would” can replace “will” in the above sentences and the results will be another grammatically correct English sentence.