The game is 4 handed and has been for awhile now. I am chip leader with around 1700, white guy in late 20s on my immed right has around 900, gamboly middle aged asian man on my left has around 1k and has been doing a lot of straddling and tried to raise the stakes to 5/10 permanently is on the button, and quiet asian guy on his left is playing around 400 at this point.

I 3x 77 utg, all 3 call. Flop Th6x4h. Checks to me, I bet 30, button calls, sb folds BB calls. Turn is 7x. BB checks, I bet 65, btn calls, bb hesitates for a moment before making it 165 to go.

The BB had been playing a lot of hands and had shown an ability to value bet light, c/r draws and bluff aggressively if he thought he could get away with it. He didn't strike me as particularly good and stated he was a live player only and seemed like he knew what he was doing. The button was playing a lot of hands and was typically aggressive, so his call did not concern me on the turn as he is always going to be putting in a raise here with a straight.

What are we doing on the turn and why?

It's kind of gross but i think all you can do is call here and call most non-disgusting rivers.

If you raise here then u shut out hands you beat and get action from hands which beat you, and you define your range pretty clearly, while being at pretty much the bottom of it, whereas if you call you keep it somewhat wider.

Sort of tough spot with deep stacks, but ya i think u gotta flat and hope for the best.

Call turn, call river. You might see him doing this with a smaller set, you may see him doing this with a FD + SD, and you may even seen two pair do this.

One could make a case for raising, but by calling you allow him to continue on the river with no REAL idea of where he's at. If he's doing it with a draw he can fire the river if he misses. By raising you eliminate the small possibility of him spazzing on the turn which is certainly possible.