PM Missed this

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At the walkthrough after the tenant left a couple of weeks ago, the PM missed damage to to lower shelf in the kitchen. He did open the cabinet under the sink and took a look, and went on--didn't open other cupboards I don't recall. Anyway, I went in yesterday morning and discovered that the shelf in the cupboard next to the sink is badly bowed from fluid damage. Half is very bad, the other half, still needs replaced, and the next cabinet floor also is warped. Looking under the sink again, now bent down and looking into it, damage can be seen on the back wall and floor, left of the plumbing, and even on the right floor of the cabinet.

The tenant cannot now be charged for that, they've sent his money back to him. the pm person said to me, "You didn't see it either."
It's not my job to see it. Who gets to pay for this repair? One man said it would be about $150 to fix. I need to get estimates.
Should not the PM person have seen this in his walkthrough?

How would you handle this?
ofgift