Posts: 521
Threads: 72
Joined: Jul 2007
In general the old HP desktop calculators are very reliable. With the 9825, the main issue is the tape drive: the rubber drive wheel will have turned "gummy" over the years and must be replaced before you can successfully use tapes. This is easy to check: just look in the tape slot and inspect the wheel; feel it with your finger if necessary. It should feel dry and you shouldn't be able to deform it with your finger.
Repairing a gummy wheel is fairly easy if you're mechanically handy. Your problem will then be finding DC-100 tapes, which haven't been made for many years. There is one company that sells refurbished DC-100 tapes, Athana.com, but they're rather expensive.
The printer's paper advance mechanism can fail, but this is less common.
Other than that, simply have him turn it on and verify that the display works.
The price you're getting is a very good price for a fully functioning 9825.