For me, it’s a mix of pre‑signup testing and observing feedback. Before I deposit anything, I often send a question via their support channels (email, chat) and see how long they take to respond, how clear the answer is. I also read reviews about customer service. In the case of 
https://sport-bet.website/ I actually tried contacting them with a small query to see how long response time was, what tone they used, and whether the help was useful. That gives me an impression if they’ll be reliable when real issues come up.