I've seen a few patients fake a seizure, although I'm not very good at catching it myself. The first one I ever witnessed I thought the doctor I worked for was being a snot about it. But low and behold, after the EMS got there, sure enough she was fakeing. The tip I finally learned was the patient was trying to hold her head up off the ground with laying her head on her arm. True seizures have no ideal or thought pattern to keep themselves comfortable while on the floor.
It is really hard to tell because some types of seizures happen when the person is conscious while some have few or no symptoms. Others are characterized by unconsciousness, convulsions, and muscle rigidity; it's easy to tell if someone is faking these, because it is impossible to. See www.webmd.com/epilepsy/guide/types-of-seizures-their-symptoms for more on this.