Very interesting thought. If I don't know a player, I assume that they are playing big hands, exact opposite of UpUpAway. For me, it seemed that every time I thought they were bluffing, they had it. But that was my experience. Yours may have been different than mine.
This.
although there are sometimes ways to spot a bluff even if you dont know the player and they are betting from early position.
today i called a bluff when i had pocket 10s in position against villain. I open raise preflop and the flop came with 8c8s6d. villain makes pot size bet, i raise 2x, villain calls. turn is 6d. villain bets half pot, i call. river is 5d. there are now 3 diamonds on the board and two pairs on the board, making any two diamonds, or any 8 or 6 into a boat. villain bets 1/3 pot. i raise to half pot size, villain shoves and i call and took down a 300bb pot. I called because although I played very few hands with him, i noticed that he entered the pot only twice since i sat down and was likely to be playing face cards. I had a loose table image, so he thought i would call him down with any two cards. he would have bet-raised on the flop if he made a strong hand and he barreled all three streets which he wouldn't have done on a flushdraw. he tried to bluff out of position on the flop and when i played back at him, he didnt want to appear weak so he tried to continue aggression when he didnt have control of the pot.
if a player is a nit, it is very easy to put them on a range. when the board doesnt coordinate with their range or show a flush draw early on, then any bet they make is probably either going to be pocket pair or a bluff. if the opponent is loose agressive, you have to have a good hand to beat them because their range is so wide that almost any board could possibly be good for them.
This doesn't mean go wild and call anything.