It's important to note that by default you should probably assume when villain checks twice to you, your turned 7 is almost certainly good. If that's the case, you need to bet big to protect your hand and get value. If he has T8o with one spade and he calls turn, he is actually not making a mistake calling turn in this instance since he has the equity to continue (almost 40% if that surprises you).
If he folds T8o with spade, he is folding out his 40% share of the pot on that turn. I'm sure you can guess how important that is for your winrate in the long run, especially since this is a common situation.