Hello. I've got a cheap Harley Benton mandolin and over the years the top sunk in very badly. The whole thing is even so flexible that you can almost get some whammy bar effects by lightly pressing the top near the bridge. I took some pictures. You can see that the top under the bridge on the treble side is depressed by more than half a cm when the mandolin is strung up and tuned. However, the warping is not so bad when theres no pressure from the strings. So I thought I might put a piece of wood between the top and the bottom of the mandolin to stabilize the area but I'm really not sure if that's a good fix. I'd really need some advice because the damage keeps getting worse and I'm afraid the mandolin will be unplayable in the near future. Thanks!