Villain is loose; a losing player at mid-highstakes. Impression from first 10 hands was loose-passive.
I think my riverbet is a little big this time...very thin for the size. I do think enough of his range calls to make a small bet profitable though. Standard fold vs unknown?
Also, turn: I wasn't sure how laggy he was but I've found (in general) most fish play their draws passively...so might want more turn value. I generally size the turn to induce and wasn't thinking too much this hand.
Finally, thoughts on flop? I think both cbetting and checking behind are fine. I wanted to keep the pot small this time to get a feel for him.
Flop I can see reason for both bet or check. On turn, I bet turn bigger, especially since he's loose passive. River I play the same.
I think that you should be betting this flop. With middle pair you are going to be beating the vast majority of his range so you should be going for value here. I don't think that you will get raised by worse often, so you should be getting easy value and hand protection here. I think your river play is alright given your read. I think the bet is fine because he will check/call worse 2-pair or even worse 1-pair here a lot, and the fold is fine if you don't think he is capable of doing this as a bluff.