But what if it's a totally new service, what would pull you over the line of trusting them/joining their site?
Nothing. I wouldn't go anywhere near it no matter what unless it involved amounts and information I didn't care about going up in smoke.
That's the right attitude. There's no need to be the guinea pig when new services launch. Let other more reckless people do that. I've seen too many incompetent operations and outright scams in this space to take unnecessary risks like that.