[Parvex]

I like bet/3bet or c/r on the flop. Don't like the call though, because you give AsKs a "free" card and you might get it in against overpairs nonetheless. So just play straightforward and see the money go their way.

His turn bet looks weak and scared, which would speak for the overpair theory. Besides that it could be the nut flush trying to look weak. Hard to say w/o reads.
Imo you have to raise here. The random NL25 Player will talk himself into calling with an Overpair and you give a free card to any overpair with a spade in it.

On the river you have no other option because he might check his overpair behind (being scared by the flush), but again might talk himself into calling.