camelCase for non-source-code files. I find camelCase faster to “parse” for some reason (probably just because I’ve spent thousands of hours reading and writing camelCase code). For programming, I usually just use whatever each language’s standard library uses, for consistency. I prefer camelCase though.
I have. My bank did a chargeback like they would if it was a credit card. I was told it would’ve been a lot harder to get my money back if my PIN was used. But, I’ve only seen that option available for in-person purchaees.