One student asked if I had ever read for someone that I felt was "evil" (her words) and what I would do if I did.
While I don't tend to classify people as good or evil, I did see where she was coming from. In movies and media we've seen stories of psychics and readers who are caught up in murder cases and crime because of their connection with either a victim or the person committing the crime. These stories are rampant and good for those nights on the couch with a bag of popcorn and a glass of wine. However, it is a really rare case when something like this happens and is usually much less dramatic.
That's it. If someone comes in your booth for a reading or orders a reading over your website or other media and you are uncomfortable in ANY way, you can say no.
I, of course, recommend being polite about it but you can simply state that you are sorry but you cannot read their cards at this time, give them their money back if they have paid, and that is that. If they insist or try and pressure you into reading their cards, then feel free to be abrupt and, if you have to, take measures to have them blocked or removed from you (most events if you are reading in public will have security or you can call the police if necessary).
Consent culture applies to more than just relationships and social encounters. Every person has the right to remove themselves from a situation they are uncomfortable in.
I've gotten every sort of client from alien conspiracy theorists, men who have hit on me in somewhat vulgar ways, people who claim to be immortal vampires from the 1400's (and believe it), tarot experts who ironically pay me so they can scold me on how I read the cards, religious fundamentalists of all sorts who believe I'm in the wrong, and more. Each one I handle on a case by case basis and rely heavily on my years of customer service training and experience in most instances. I'm also blessed to have a husband who can look pretty intimidating when he chooses to and is often with me when reading face-to-face with others (its nice to have personal security).