Sort what is on offer into three groups before negotiating.
Safe: glass without electronics
Eyepieces, Barlows, diagonals, filters, finders, dovetail bars, counterweights. Check for fungus — a branching pattern inside the glass — and for coating damage. Beyond that, these last decades.
Careful: tubes
Look at the mirror coating for lifted or clouded patches, and work the focuser through its whole travel feeling for roughness and sideways play. A worn focuser is repairable at a real cost; a deteriorated coating is a recoating job.
Risky: anything with a circuit
GoTo mounts, motorised focusers, cooled cameras, dew controllers. Ask to see them work. A mount that cannot be demonstrated is being sold on trust that the price should reflect.
What is missing is part of the price
Counterweights, dovetail bars, the original diagonal, the eyepieces it shipped with. Each has a replacement cost, and a listing that omits them is quoting for less than a complete instrument.
And the question that settles a lot
Why is it being sold? An upgrade is a good answer. A fault that was never traced is a reason to walk away.
The questions that keep arriving
Are eyepieces safe used?
Among the safest purchases there are. Look through them at a bright even surface for fungus and separation; scratched barrels are cosmetic and universal.
What about a used GoTo mount?
The riskiest item on the list. Ask to see it slew and complete an alignment. A handset or a motor board that has failed is frequently not economically repairable.
Last reviewed 17 September 2026