Here's how to tell when she's faking it.
She's not speaking in tongues
Sure, coherent dirty talk during the deed can be a clear sign that you're on the right path. But when a woman orgasms, she's incapable of reciting Wordsworth. If she's really getting into it, her phrases are going to break apart in -- to -- lit -- piece...
If all you're getting is "Come for me," or "You feel really good," or all her noises are synced up perfectly to each of your hip thrusts, you have a right to be suspicious. Yeah, it may seem like a porn set -- but remember, those ladies are acting, too.
She's saying words like "faster" and "more"
Sorry, this is her telling you to get on with it and get off. No woman approaching orgasm is telling anyone to hurry along.