That seems for the most part to be surface rust and not a problem. It's hard to be sure on the small amount of chassis rust.
Not that I'm a perfectionist, but I'd use it as a bargaining chip and see if you can get the price down a little. Doesn't look bad to me.
One thing you can do is check is see if this vehicle (in American trim) has any recalls of consequence. There are a few Toyota trucks with chassis rust recalls.