Models, if you’re struggling with posing and expressions, and can’t get through a shoot without “freezing up” because you’re so nervous, then chances are you shouldn’t be asking to get paid. It might also be wise to
Typically*, photographers pay models that have something to offer them (when they’re hiring models for things like private projects and portfolio building–when it’s a client that pays, this may be a different story). Chances are, if they hire a model who’s nervous and constantly gets stuck posing/emoting, and ultimately has one look and a handful of stiff poses, they’re going to feel a bit short-changed at the end of the day.
Just some food for thought.
*Note: I did say typically. Some photographers do hire based on things like looks and measurements before they hire based on experience. But many feel that a model needs to have something worth paying for in order to be, well, paid.