A suggestion for OP. Hope you could be as transparent as possible when deciding the winner or someone gonna complain if he doesn't win.
in essence, they don't have to explain much. which design they will like is a completely subjective matter, they pay for it, and will probably choose the one they think will best represent his business. they certainly won’t opt for a different design because someone complained.
Of course, they also accepted submissions through PM, perhaps that part is not the most transparent, but it is their decision and all participants are aware of it.
btw. it will be a very difficult choice here, a lot of good work. at least he would be to me.