What Would Have Happened
The third, or 'past', conditional is used to imagine past outcomes different than what actually took place. This conditional is used to express what would have been different if a person had done something differently.
'If' clause - past perfect + , + result clause - would + have + verb (conditional perfect tense)
"If they had known our recipe costing formula, they would have implemented it."
She wouldn't have agreed with her business acquaintances if she'd know the whole story.
She wouldn't have known of the problem if the debts hadn't forced early hotel check-outs.
She would have cut out seafood if the shrimp had been found to contain mercury.
Examples of Past Unreal Outcomes
Do not use a comma, when placing the result clause first.
She would have sold the luxury properties if the economy had continued to grow.
She would have trained as a food service professional if she had got the job.