Performance loss in used amplifiers?

If it has any electrolytic capacitors and the unit is ten years or older it would be useful to have a tech check it out as this is a very expensive piece to service if it breaks. Same thing for tube preamps/amps, too.

The switches may get dirty over the years with many units; don't know if this will happen to Levinson.

One more thing to look for: get a closeup picture of the PCB. Look closely for any sign that the unit has been modified (tampered with, upgraded). You can usually see crummy soldering; if you can't at least the job was done neatly. Always ask the owner if the unit has been serviced by anybody other than an authorized service tech.

And...when buying a used preamplifier be very specific when asking if it works correctly. For example, if it has a phono section and a headphone amplifier have the seller explicitily advise you that both features work correctly. I have had sellers tell me "oh, I did not have a turntable so I could not check the phono". This was after telling me it was mint and all was well; not. I have a dispute going at the moment on such an issue.