WSOP ME hand #3 - My cards are basically face up on "scary" board

[billyjex]

Main villian in this hand arrived 30 minutes late. He has been at the table for 10 minutes so I really have no read on him, other than he hasn't really done anything crazy in 10 hands.

I have about 7500 chips to start the hand. I doubt he has any read on me either.

Level 1, 25/50 blinds.

He limps in the hijack, having me covered. Button, a tight solid player, limps. SB completes. I look down at black kings and raise to 300. Only villian calls.

Flop is A 9 7r. This seems like a WA/WB situation, although there is some straight draws out there. I decide to check here and play conservatively. He bets 500, I call.

Turn is a 6. I check, he checks.

River is a 5. I am really lost now with a 1750 pot. I check again, basically signifying I have a big pair lower than AA and hate the board. He throws out 1500. Call or Fold?

Looking for advice on previous streets as well.