The tire 'beads' on the edge of the tire (the horizontal surface when mounted), that surface should be as smooth as possible but I don't think you need a machine finish. The outer surface of the tire near the edge will mate against the bead stop (vertical surface when mounted, this is where the bead lock be if there is one), that surface does nothing for sealing the bead.

Gunk, Slime, TireSeal - whatever you want to call it works quite well for sealing the tire if the bead is questionable. The only problem is that the guy installing your tires will hate you for using it (just blame it on the PO).