[Pog0]

Obviously with an underpair, if you're calling on the turn with the belief that your hand may be good, then a fold on the river is unacceptable. I was about to make a comment to that effect on this hand but you have at least 6 outs to a great hand and possibly even 14 if you're behind.

I think this hand is particularily tricky because if you're behind, you may have 14 outs to to the best hand (suppose he paired the ten, then he has less than 1 in 4 of holding a spade), while if you're ahead, there's a good chance several of these cards you think would make you the best hand actually make him a better hand (if he has overcards for example, there's a better chance he holds a spade and then those outs you think help you actually help him).

a. You don't improve, neither does he, he bets and you fold.
b. You improve to a straight or flush or set, but he improves to a better straight or flush in the process, he bets and you call.

The possibilities are so great that I'm either folding to the turn bet or calling the river bet regardless (I think your line was best though). There are very few hands that if turned face up on the turn are worth folding to. Pocket sevens with a spade is one of them.