Took me 6 hours to realize the stud finder was right all along

Started hanging shelves in my hallway last Sunday and the stud finder kept flashing false on this one spot near the corner. I moved it, recalibrated it, even borrowed my neighbor's unit, but it kept showing the same thing. So I ignored it and drilled into what I thought was drywall and hit nothing, just a hollow thud. Then I tried another spot and blew out a chunk of plaster, which made a mess I had to patch. Finally I gave up and cut a small hole with a utility knife, and there was the stud exactly where that finder said it was, just painted over twice so it read weird. My whole afternoon went to doubting a $30 tool instead of trusting the beep. Anyone else ever fight their stud finder and lose? What do you use when the walls are hiding something?