Could’ve — Should’ve — Would’ve

I think it’s due to the sound here, but a lot of writers are making a real error when they write out could’ve, should’ve, or would’ve. 

Yes, the letter f can have the sound of v, as in the word of. 

But.

These phrases are just plain wrong: “could of,” “should of,” and “would of.” 

could’ve = could have
should’ve = should have

would’ve = would have