villain total unknown
PokerStars 3/6 Hold'em (5 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

Preflop: Hero is MP with 8, K.
1 fold, Hero raises, 2 folds, BB calls.

Flop: (4.33 SB) 6, 4, 7 (2 players)
BB checks, Hero bets, BB calls.

Turn: (3.16 BB) 6 (2 players)
BB checks, Hero bets, BB raises, Hero folds.

Final Pot: 6.16 BB

With no read I say take the free card - if you're willing to put in a bet here anyway and you think he's capable of making a bluff, you can pay the same price on the river to show it down and get some info. If he's not, you have a shot at hitting your draw and you can fold if he bets and you miss.

I would check the turn and take my free card, this is the type of flop which will get check/raised very often when playing against a BB who has defended their BB. If he calls this flop, he typically has a piece of it and will not be folding to a bet. It's a small pot and really not too worth fighting for. The only hands you beat are hands like JT which decide to peel with overs, in which case you may get a free showdown anyways without having to put in another bet.

that gives JT J9 QJ etc. free cards
also I get KJ/KQ type to fold a lot
and get free SD vs 5x etc.
checking would be better with an AJ type hand that can pick off all the bluffs.
Checking turn and calling riv UI seems kinda bad to me.
bad part about betting is I give up my chance to suck out (or dont' take it for free). So the gutshot I have makes it close I think.

Against an unknown, I think you need to take the free card.

You bring up good points, but against an unknown you don't know for sure how much or if your points apply to your opponent's play.

Check behind on the turn, call a river bet unless its a 3.

With the board pairing a ton of players will checkraise with draws, air, or any pair hoping to get you to fold overs.

yes, this is precisely my concern, but checking with the intention of calling with K high UI felt fishy to me.