There is a ripper Silvia right here....http://coffeesnobs.com.au/YaBB.pl?num=1226218318
Sold and backed up by a CS sponsor, and lovingly owned by a CSer.
With a PID fitted too.
Silvias are rock solid machines, there is planty of great internet "how-to" info available and they are dead easy to work on [provided you are mildly "Mr-fixit" inclined.]
As far as day to day & year to year useage goes Silvia should be regularily cleaned, backflushed and descalled.........you could / should ask the seller if or how often these actions have been done.
This will not really tell how good the unit is but will give an idea of how diligent the owner is....The Response [if public] may also dampen buyer confidence
If the unit is listed in good working order, then everything should work and you should have some recourse if something is wrong.
That said they are a very hardy machine.
At three years old you would probably expect to change the group seal, easy to do, would cost approx $6.00
Check with the seller as to whether this has been done.
Otherwise the common problems/pitfalls/wear & tear issues that spring to mind are:
Pump: pretty unlikely to have failed [I replaced mine at 5 years as a general update, it seemed to working ok] cost = $60 and a 15min job
Steam Valve: could be blocked, tight or leaky, mine is still good @ 5+ years so I dont know the cost. Its apparently an easy change and at a guess would be less than $50
Three way valve and Solenoid If these failed it would be most likely due to lack of cleaning maintainence. Again easy to replace, I dont know the cost, but either part would be under $50 [guess]
Element: This would be the most expensive repair, newer Silvias [perhaps the one you are considering] need the boiler and element replace together.................the cost of this [I think] is $200- 300.
If the boiler is not re-filled "primed" following steaming the element can burn out.
Bear in mind that if any of the above issues were present, you would have a pretty strong case to argue that the machine was not in perfect working order.
So I reckon a safe bet, but bear in mind you will get no support from the seller, compared to if you bought a new machine from a CS site sponsor.
Also remember, it will be basically useless until you pair it with a good grinder...............preground supermarket coffee will gush right through it.
But, You would get away with freshly ground coffee from: CS green, Veneziano, Cuppacoffee or other site sponsors...see left <......
Good luck with whatever way you go, I guess well see you round here sometime, so let us know.