Yea, the first cum has to be a fuck unless you know you can suck the life out of them with your bj skills.
Have a chat. If they don't think they can manage they usually mention during the chat that they cannot manage a second and either end the meet, or carry on chatting.
If they can or haven't said anything, start stroking his cock. He will soon let you know.
Be wary of the time. One of my regulars can fuck easily non-stop for 40 minutes. The second cum with him in the hour is not possible. The first comms with him was about the 2nd cum. The first time we met, we fucked for ages. Had a break and he wanted to go again with 5 minutes left. Obviously wasn't going to happen.
Another one can cum 3 times within the hour. He fucks very, very quick. Have a break. Oral and he cums quick. A quick break and a quick fuck. He's not in a relationship so he either saves it for me or has a wank lol. And we still have about 15 minutes left.