When I play holdem I "usually" pay people off when I have the second nuts. Most of the time I find they didn't have the nuts after all and although I havent tracked it (I know I should) I'm willing to bet that I've won more money than I've lost by calling down with the second nuts. The biggest example of this is the K high flush, I know it's possible that people have the A high but I usually call anyways and I've only lost about 2 out of 20+ times.
As stated before though you have to be aware of the board, on a board of JTK6J your straight is no good, as many players love JT or JK so someone probably has the Boat, just one example.