Mellotronists

The best bet is to have a friend who already has one or is familiar
with the workings to coach you along with your purchase. I'd say first
off, the cosmetic appearance can tell you if it's been knocked around
a bit. Do the keys lay flat and level like a row of straight teeth?
Look for major dents in the corners that might imply a dropped
unit/tweaked -unsquare cabinet. Ask the seller why it's for sale. That
question almost sounds personal, but this is a major purchase...and
the answer may say a lot. I can't conceive selling a 'tron unless I'm
in total dire financial straits. Ask about the history of the machine
and how often it is/was used. Has the seller ever had to buy/replace
parts? Where did the extra racks come from?

Then of course turn on the machine and check the sound of the
mechanics, and run through all three racks note by note, all three
selections to the full eight seconds, and with the top off, note how
they retract and the fidelity of each sound is. The motor/flywheel
should make the light whirring sound of a well-oiled machine. Ask if
the seller ever demagnetised the heads/gave the unit regular
maintenance. Do the pots sound scratchy? There's so much to say here
without being there with you when you make the purchase, but a lot of
the little things that typically go wrong are usually easy to fix and
adjust. If the sounds through the seller's amplifier/speaker system
sound good and steady to you...that's the happiness factor right there.

If this is the craigslist unit offered w/the muff and racks in the Bay
Area, I'd say that sounds like an okay deal to me if all is in working
order. From just the vibe I get about the way the unit is presented
(the muff case is a good sign that the owner is conscious about
protecting the unit), methinks you'll be our newest happy 'tron owner.