Long time lurker here, thought I would drop what I look at before signing up anywhere. After a few bad experiences I stopped going by ads alone.
First thing is the licence: check who regulates the site, and whether they actually accept players from your country. After that I look at banking: card, e-wallets and bank transfer should all be there, 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 live tables often do not count at all. A good recent review that covers all of this is worth a read here Lilibet Casino review and it saved me some time.
I play almost only on my phone, and if there is an app I make sure it comes from the official page. Support matters too: if they answer in a couple of minutes that is a good sign.
Hope this helps someone. Only play with money you can afford to lose.