I may not be that experienced in diving, but I always make it a point to question the DM DURING the dive briefing if I feel that not enough information has been given. I have, on a number of dives in Australia, insisted that the DM went in with me and my buddy when I am not so sure about the dive site. I have also, on other dives, insisted that DM went in with me and my buddy when I am not comfy with my buddy's diving style.
I know I have a lot to learn still, and am always happy when I talk to other divers and learn from them. I have no problems with my buddy leading if I feel that he/she is reliable. How can I tell? From buddy checks (which I always insist) to looking out for each other underwater. Usually one can tell from the first two dives with a buddy whether you can depend on him/her in emergencies. I don't admit to having been an inexperienced buddy once to some other divers (when I first started diving), but I have had my taste of bad buddies who followed fast fish and went missing round every corner to know what not to do when buddy diving.
I've since learnt to be alert in working with stranger buddies. Talk to my buddy before the first dive about the dive plans and hand signals etc, and before every subsequent dives. I have frequently dove with strangers, and am now very attuned to tiny actions and reactions that tells me alot about their diving style. If I am not comfortable, I made sure a DM teams up with us. Tough job for the DM, but safety is everything to me when diving.