Welcome Paige. Here are a few I have run into:
1. Guests who don't have a profile photo of their face.
2. Guests who want a discount.
3. Guests who are booking your place for an odd reason. Case in point, our cottage is best for people who are traveling through the area, young couples on a budget, and single travelers. I got a reservation from a man surprising his wife for their wedding anniversary. She was not happy and I had to refund them. I don't think he fully read the description or knew his wife.
4. Guests who don't introduce themselves or are cagey about personal questions. You don't have to ask for their social security number, but I like to know a little more about their visit and if I can help them.