These don't have traditional studs like a house, making them hard to find. I ran into issue s with mine when replacing a shower rod because the stud at that location ran horizontally instead of vertically so the new rod missed it.
I'm not sure on the Salem's, but in my Flagstaff I believe the studs are hollow metal tubes so the studfinder's not finding the density difference to pick them up. (Mine's a cheap $7 finder and couldn't find them either.) But I have had some luck with the old 'tap' method. I.E. tap on the wall finding the spot that has the least flex. Most likely it's a stud.
There's no use crying over spilled milk, unless it's on your keyboard.