It needs to be waxed at least annually. If left to weather it will never come back to bright again. Even compounding won't bring it back. If the topsides are severely chalked the boat may need to be painted, or be happy with a dull finish. Look at the woods on deck.
Most boats now use teak exclusively.
If it's varnished, and looks good, then you know the boat has been well cared for. A fresh coat of anything indicates the owner cared for this vessel. Teak neglected is unsightly. It doesn't have to be varnished or Cetol'd, but simply cared for. Some folks like oil.