Call this river bet?

[spydog]

This hand shows why reads are so important to squeezing out the mostest EV. Against an unknown, I think you played it perfectly, assuming you called the river bet. However, if you had the SB pegged as a TAG or at least a tight raiser, then I think the river is an easy fold because there wouldn't be any hands (apart from KQs) that he could have raised out of the SB preflop that you beat.