You'd think a tag would raise a good hand like 2 pair+ at some point, especially the turn. So it prob means he's weak or on a draw, which means a river bluff could work a lot, but 50%? In my last thread you wrote that big river bets look like bluffs...so why not bet river like 1/2 or 2/3 pot?

Another possibility is he sees you as a maniac and called down to induce this. That turn bet does seem committing. Being oop definitely sucks. I'd wait for a better read/situation for 3 barrells but I'm more conservative. Do you find this works a lot of the time?