Fairly new, under 50 dives, I'd have zero problems saying that I wouldn't be comfortable diving a triple. It's no fault, no foul, an honest recognition that you and your buddy aren't up to the skill level/awareness/comfort to do such a dive with an unknown person. Honesty is often the best policy, while the politically correct delivery is not to say the other person looks like a walking disaster, but that you don't have the right skills developed yet.
I'm still wet behind the ears, have a buddy I've done 30+ dives with. Both AOW. We've only done a triple once, an area we had been to many times, had already done two tanks that day. In such a case I played third man, purposely hung slightly back, as I always dive with redundant air (pony), could keep an eye on both my regular buddy and the other person to make sure they were having fun, no problems; we dive often enough that even with a few feet of physical separation we are constantly doing checks on each other. A good experience, but that was because we consciously chose to invite the buddyless person, idle chitchat indicated that they had decent experience, they were good on gearing up, and we knew the divesite conditions were excellent. I guess others have hit it, "Plan the dive, dive the plan."
Where in upstate NY? I go up to Alexandria Bay many weekends, or the Ogdensburg area, looking to pop over to Kingston next weekend (we were there last weekend, good diving).
Of course, if you were the Kraken, you could say "I'm sorry, but I just put a pee valve in my wetsuit, am embarrassed to use it around strangers."