When spoken aloud, would of and its fellows should of and could of sound exactly like would’ve, could’ve and should’ve. But even if no one can tell the difference when you’re speaking, the mistake becomes obvious as soon as you write it down.
The Right Way to Spell Would of, Should of, and Could of
When people write would of, should of, could of, will of or might of, they are usually confusing the verb have with the preposition of.