Strange postflop example from Jonathan Little's "Poker Workbook" that I don't understand:

7-way, blinds at 125,000/250,000 with a 30,000 ante, everyone folds to the small blind, a good, loose/aggressive player with a 12M effective stack who completes. The big blind has Ac9d with 26M and raises to 850K. The small blind calls. Pot 1.91M.

Flop: Js8s4c. Pot 1.9M. Small blind checks. Big blind makes a standard c-bet ~1/3 pot or 700,000. Small blind calls.

Turn: Js8s4c6d. Pot 3,300,000. Then check, check.

River: Js8s4c6dTh. Pot 3,300,000. Small blind now bets 1,800,000 >1/2 pot from his 10,850,000 stack. The big blind then raises to 5,000,000 (1/2 of small blind's remaining stack).

Spoiler: Small blind folded Kc7c to the big blind's river raise, so both players were bluffing. But I'm confused as to what each of them were 'representing'. My first instinct is that this was a trap by the small blind with the flop & turn checks trying to induce bluffs (but what was his bluff-catcher?). I assume then that this is 100% fold-equity play, by both players.

I would love to see PIOsolver's analysis of this hand, if that is doable (by the way, I know zero about PIOsolver).

Did you do any of the ‘homework’ yourself?

What’s SB’s complete/call range, does BB raise a polarized range against the complete?

FWIW, I don’t think SB can c/c the flop with K-high and two backdoors unless he’s optimistic about his chances to take it down on the river if the turn checks through.

I haven't personally studied open completion ranges from the SB with antes in MTTs, but pre-flop seems reasonable by both players.

On the flop I'm not sure the c-bet is standard. SB definitely can not fold here with an overcard and multiple backdoors, but I'm not sure if raising or calling is better. Given the very small c-bet sizing calling seems fine.

SB has to bet the river with air after taking this line. BB thinks he has a good candidate to bluff with his 9 blocker.

SB represents a jack (or better) by limp-calling, check-calling, the turn checking through, and then leading the river.

BB represents JTs (two pairs) or Q9s (a straight) or something like that, by betting flop, checking the turn for pot control with a weak one pair or to take the free card with a draw.

This hand will be discussed in-depth in my podcast Weekly Poker Hand, Episode 215, which will be released this Thursday.

I dislike the big blind flop bet and the river raise size, which I think should be fold/call/all in decisions. River bluff range selection seems ok on the surface, but since I don’t have this hand in my river range I think AQ no spades makes a better (top of my folding range bluff) candidate.

Just subscribed, looking forward to listening.

If I didn't see the cards this is how it would look:

Preflop: SB completes, BB tries to steal since SB obviously didn't show any strength. Standard move. SB calls correctly seeing this as a steal attempt and K-high is ahead of a random hand that tries to steal.
Flop: c-bet, call. Nothing has really changed from preflop in terms of information. If SB calls preflop there is really no cards he would fold to postflop.
Turn: check, check...SB has given up/wants to get to showdown cheap, BB isn't sure whether SB has a little something (or might be sandbagging)

BB has Ace high which is perfectly good to check to showdown if SB has indeed given up. If he bets he will only be called by better.
River: BB showed weakness on turn, so SB takes another shot. The ten didn't change too much. BB sees this as for what it is. Barring a random Tx or Q9 or 97 there are no hands that improved the SBs hand to the point of betting for value. BB has nothing but can get Ace-high or even a random 4 or 5 to fold with a raise.

No one was really representing anything. Everyone was aware the other one was likely bluffing or had a very weak holding. BB just asked the question on the river "are you sure enough I've got Queen high (or K2, K3, K5) or worse to risk being crippled?"

I find the bet sizing by the BB on the river interesting. He puts in just enough chips so that SB can't really shove-bluff without giving BB good odds to call.