If’ usually introduces conditional clauses. The same applies to other conditionals such as unless, should and in case which, however, perform other functions in different contexts.

Conditional offers are used in real estate transactions when a buyer’s offer on a home is contingent on something getting ...

With this combination we are contrasting an imagined or real event in the past with the ... of past event and present result by using type 3 conditional (if + past perfect, would've + past ...