I don't know how to deal with the donk turn

[Wynton]

Somewhat common donk-situation has been throwing me.

Say I raise in mp with something like 99. Only bb calls. Flop is A83, rainbow. He checks, I bet, he calls. Turn is 6, completing the rainbow. He bets. Is the best line here simply calling down?

Suppose the turn was an overcard, like a J and villain donks. What would you do here?

My tendency has been to give the donker credit for a decent hand, but I wanted to check whether this makes sense, at least as a general rule.