you have to give yourself financial room for the worst case scenario for repairs. I like the suggestion of offering 1/3 of what they sell for in very good condition. Typically many already had it evaluated and know exactly what is wrong with it and how much it would take to fix it.
Another suggestion is to tell the seller to get it evaluated and get a price to repair it and offer to split the cost to repair it.
Take for example a Mark Levinson 23.5 amp. There is a very good history of what the used price is for a good working unit. If one channel is out, The price to diagnose and repair can be substantial, depending on what is wrong. But, if the sale price is low enough, I would jump on that unit in a minute and fix it myself or send it to George Meyer AV in LA and have them fix it. However, then you also have to consider whether the caps should be replaced also.
I think the price of the unit is question is too high for one that isn't working and also since I have no clue what is exactly wrong with it and how much it would take to fix it. So, about $1000 or less for that non-working unit sounds right to me.
enjoy
