How to know if someone likes it rough or is into S&M etc.

iv been having really good sex with a partner and spanking and hair pulling is one thing, but grabbing my throat was a little concerning I asked him to stop and he did straight away and he does respect any of my boudaries im just wondering if it was a spur of the moment thing or if this is a sign hes quite heavily into rougher sex, he has hinted and being quite dominant (which I do like to an extent)

It takes a lot of trust to play that game. It's like seeing how close you can get to the edge of the cliff without falling off. I doubt any of us here can predict what he is capable of doing. The risks are that he might misunderstand what you are willing to participate in or even worse, completely lose control.

In any sexual encounter, both people should understand the other person's limits and respect them as he has done but I suspect writing a script beforehand would take a lot of the thrill out of it for both of you.

I would try to figure out what there is about my personality that makes this behavior appeal to me.