My studfinder feels flaky. (I live in an old apartment with lots of plaster spots.) I just used it and was disappointed that the studs it may have found (beeped on 2 out of 3 passes) mostly didn't line up with the brackets on the furniture I wanted to mount ans the spot I wanted mounted.
So, I actually screwed wood screws into the wall in the places I hoped it was wrong about. The studfinder was not wrong, at least not about negatives.
The only stud was way on the left here, which was one of the spots I wanted them to be in. The studfinder said there were no studs in the other three spots, and there weren't.
I updated my placement and shifted everything to the left to align the holes with two of the studs it said existed (and to miss the stud on the left). One of the spots did have a stud. The other spot had something…rubbery? behind it.
I might have to go with just one wood screw and three anchor screws.