Reckon it's different if it's a date out of the blue to people who have a lot in common for starters (eg meeting at work/uni).
I think it's basically a learning experience in the first few dates to see how the other person conducts themselves/if you're socially compatible.
What I don't think works is thinking there are hard and fast rules or "tests" or "signs" to prove that someone is going to be a good guy or good woman and you're going to live happily ever after.
Eg: pays vs not pays? Assertive vs non-assertive? Very open and extroverted vs a bit quiet? Casual vs scruffy? All of these could be signs of...well...absolutely f**king anything.
Of course if there is a pattern then red flags can build up, but one date isn't enough for a complete picture (although sometimes it can be enough to think "nah")
I've gone on dates with very tight, wannabe cocklodger types who will insist on doing the full works and paying extravagantly for them on first dates.
Or a first internet date with someone who arrived early, had picked the best seat in a well-chosen cafe, called me when he was there to tell me he was there. Went fine. Second date, he was late, incredibly hungover, and yawned through the whole thing without being apologetic. The "consideration" was something he brought out once only.
You have to keep your judgement open, there are no short-cuts to discernment regarding people.
I often hear people repeat things like "I knew he/she was perfect when they did X" and actually that really is completely irrational, you have to look at the complete picture?