Ask for a photo of the rear brake bridge. If it's a Roberts then it will have a little "R" embossed into the rear brake bridge:
Never seen one from the 80's without that.
Usually they'd have something stamped on the fork crown too but, as Ecobeard says, I suspect the forks aren't original. You'd need to ask the seller for the serial number from the forks to check that.
Either way, the paint job and decals are not original.
Ask for a photo of the rear brake bridge. If it's a Roberts then it will have a little "R" embossed into the rear brake bridge:
Never seen one from the 80's without that.
Usually they'd have something stamped on the fork crown too but, as Ecobeard says, I suspect the forks aren't original. You'd need to ask the seller for the serial number from the forks to check that.
Either way, the paint job and decals are not original.