Hello Ken,
If the machine is more than 5 years old and the seller should tell you this, be aware, components may be working okay but there may be massive limescale build up round the heater and drum and bearings, no way to check this really, but ask or find out if the seller is in a hard water area, I would not buy a used machine more than 1 year old personally.
Ken
drivewithken@blueyonder.co.uk, August 2007