how to tell what trim package a prius has

You will need the VIN of the vehicle you're considering to do this:

Go to THIS website and enter/submit the VIN. You'll get all the specs for that car.

 

I've posted a few times before that the website linked above has the wrong trim for my VIN.

I got curious when I bought the car and the seller had it listed as a V when it was positively, unmistakably a IV.

Then I put the VIN in to the Toyota owners' site and the site said it was a V. So at least the seller wasn't scamming me; he probably just used the same website and believed the result.

I don't know how to explain a mistake like that from Toyota's own website, but it is clearly not completely reliable.

The best approach is to learn how the different trims were equipped, and compare what the car has.

 

I would first go to the Toyota site with the vin. Otherwise you look at the trim feature and option list. For example a trim 5 will have LED headlights. Leather seats can be dealer added or even bought off ebay (they are really custom made seat covers and are a synthetic called Softex).

This is from a Prius v brochure. Some items vary by year and model (Prius, Prius v, Prius Plug In), so this method can be tricky without the exact list.