Customer red flags

What are some customer behaviors that you as a seller consider to be red flags? I see a lot of comments on posts here where a seller has had an issue with a customer, and a lot of people will point out that something that customer did would have set off some alarm bells and they would have canceled it. After having my fair share of crazy customer interactions, I’m just curious about what you all consider to be a red flag early on, and what you’ll cancel orders for!