Against this fish I think I'd be checking back or betting small like $4-6 to target 5x and PP. Really hard to see what they call if we make a half size bet or more that we beat. I'd expect even bad fish to fold pocket pairs 66-TT by the river for anything more than $6.

A fish can have a lot of things which may include a Kdx hand. Also a J of course. If he's a bit unpredictable/slowplay fish type then in this spot I think I might check back as we don't get value from a lot and there may be a lot of those missed FD type hands vs a fish. The reason I check instead of betting small is because if this guy decides to x/r us then it's a bit disgusting because as much as a small bet can induce a bluff raise here, he can do the same with his jacks/flush maybe and we might be stuck wondering what to do if this happens. But I think if we do bet then it has to be way small. I think Harvie's sizing sounds good if he is sticky with most pairs.

If our opponent is so bad I'd make it bigger preflop and bigger flop and overbet ship turn. Maybe I need to slow down sometimes!

As played I'm siding with Harvie and I'd bet the river for around 20-25%. Doesn't matter to me if I get raised and have to fold, just gotta get value from these guys is all.

Pre: Standard. This sizing would be my normal sizing when three betting IP but if villain is an absolute fish we can look at going larger here.

Flop: Again normally I would be going for around half pot when c-betting in a three bet pot but vs a fish the norm goes out the window, I see no reason not to go larger here when we can expect villain to be making some terrible calls with hands we have crushed.

Turn: Same advice as flop, larger is better here I feel.

River: J kind of sucks, I probably just check this back. I don't hate the above suggestions of check folding but checking seems superior to me since villain is going to have so much Jx in their range.

I'd be making this closer to $3 pre against such a player.

Flop and turn should both be bigger. No reason not to.

I would check back the river against an unpredictable opponent who might to something ridiculous if we bet tiny.