US equipment uses 115 volt power and should not be plugged into your 220 volt supply. However, some second hand gear will be due for a checkup and recapping, so if you can get it to a Naim dealer or importer, they can check it out and make the small changes to the power supply so it will work for you. Do find out how old it is and if it has been serviced (generally a good thing).
I have had success with a purchase via EBAY. I bought from a Canadian dealer who was discontinuing Naim. Someone posted on this forum that an 82 was being offered on EBAY, and I put in a bid. It was exciting waiting to see if I was going to get it, as there were other bidders, but I put in a high enough cap (not a HiCap) and got it at an excellent price.
I was also happy to be dealing with a (soon-to-be ex-) Naim dealer, rather than an individual, especially as the transaction was international. I live in the US.
There have been very few posts on the forum reporting problems with second hand purchases. However, one guy was having problems with his second hand preamp and it was clear that someone had tried to change the internal wiring to the preamp power connector. It was no suprise that the preamp was not working. A demo is worth a lot in this situation.
Simon