NavList:

On sextants that sound "too good", first, yes, look for signs that it's a replica. Find some photos of C.Plath sextants in the same decade. Any sextant can be converted into a "C.Plath, Hamburg" replica sextant with a little etching on the arc. Easy! But the rest of the sextant will clearly be wrong.

Another concern: is some really critical component missing? Make a list! For example, if the index mirror frame is gone, it may be difficult to repair --probably a deal-breaker. On the other hand, if perhaps the index mirror is cracked, that can be fixed and would earn a modest discount in price. Check the main shades --in front of the index mirror. When you try to look at the Sun through the complete set, it should be nearly or entirely invisible. When you find the proper combination of two or three shades out of the full set, you should find the Sun comfortably darkened and easy to look at for minutes at a time --no bright glare at all. Many sextants, either because they're replicas or due to a bad repair or in some cases due to unusual age decay end up with shades that are insufficient for viewing the Sun. That's probably a deal-breaker, too. [btw when looking through the shades at the Sun, swing them out of the primary light path so they are "over the shoulder" of the sextant... then you can look at the Sun easily without the telescope and with no adjustment required]

Please feel free to "text" me photos of the instrument while you're examining it at 401-644-6012. I can't guarantee I'll be around, but chances are good. If I am, in fact, available, I would be happy to give you real-time feedback and help you decide. If it's an unusually good deal, you have to grab it quick.

Frank Reed
And don't forget to sign up for my online workshops: https://ReedNavigation.com. :)