Buying any used machine is a risk. If you can find a local one it would probably be better, that way you could see it working and do the trade hand to hand. A friend of mine just bought an Excalibur 1000 on ebay, it had to travel half way round the world and took some 18 days,(who knows how many dents and bangs it got in transit) when it arrived it didn't work as the battery was flat, on charging it it only worked for a brief second then died, he took it into a local shop and they tried a new battery and it powered up ok. I sent him one of my new 1400mah fully charged batteries to give it a proper try, when he tried it it works but intermitently once you start to move, seems like its has a battery cable fault too. Rather than send it back at great expense for a refund(and loss) its gone to the minelab dealer to be fixed, the seller (give him his due) refunded the price of a new battery & pod as the old one was cracked and has water inside, the machine looks clean and dry, we'll see the outcome when it comes back, hopefully they won't find too many faults.
Having said all this lots of guys as already mentioned are good and honest, this may be a one off, any machine can work one day and fail the next, You might pay a little more for a good trade in but you have some peace of mind from people like Richard(its only a pity for me as i'm not in USA or i would have bought from him a few times, minelab rules®s don't permit)I had to buy my second excali and etrac new.
Take into consideration the cost of a trip to minelab added to the cost if you buy second hand(just in case) like Jim
Be patient, one will turn up sooner or later and from a good source.