Their readings often focus on emotional states and past life connections. They will also counsel about possible health problems. The attendees are NOT all true believers. The most common means is to provide minimal or misleading information. I've found that altering your attire is also very effective at assessing which ones are just going with visual and behavioral clues.
Samplers go to as many different readers as they can afford, asking the same questions of all.
In comparing results, a sampler may become a convert. It's not unusual to see a client having an extreme emotional reaction in the midst of a reading. We told him we'd been to the psychic fair and he assumed WE were psychic readers. We ended up reading palms for him, the hostess, and one of her friends.