Been reading this board for a while, thought I would drop my short checklist for choosing a casino site. After a few bad experiences I learned to read the small print first.
I always start with licensing: find the licence number and look it up, and if your country is on the allowed list. After that I look at banking: I want at least one fast e-wallet option, and cashout times should be listed up front.
Never judge a site by the bonus alone. Read the wagering and the max bet rule, and some games count less towards it. A useful overview with bonus rules, app info and payment methods is worth a read here Winzter so you know what you are signing up for.
I play almost only on my phone, so I check how the lobby works on a small screen. Test the live chat before depositing: if they answer in a couple of minutes that is a good sign.
That is about it. Only play with money you can afford to lose.