[kroeliewoelie]

This is a horrible fold. You are getting 3 to 1, so you only have to win 25% of the time to break even on a call here. There are several reasons for villain betting the river:

1) value betting Kx
2) bluffing because you look weak
3) value betting 8x,9x,Tx because he thinks you cannot possibly have a king

In the first scenario you are beaten, but in the other two you are good. And scenario 2) and 3) definitely happen more often than 25% of the time.

So instacall.