If the bezel had been removed at any point there'd probably be a gap between the bezel and the back of the device. If you turn up the frontlight to 100% and then go in a dark room see if there is any light spilling over the sides.
It shouldn't be possible to tell from the front, the bezel is very flexible and does not take damage on removal, it's the glue/water seal between bezel/display/and back that turns "lumpy" on removal so it's not a perfect fit afterwards. Or at least that how it was for me.
There's no harm to the reading experience. As for the waterproofness you should not trust it too much anyhow.