I've bought items from J Levine's online and live auctions and even sold a few pieces through them in the past couple of years.
AUCTIONS
There are so many awesome items and it is always a great selection. It's fun to peruse their selection online for the weekly auctions. I'm really looking forward to their big New Year's Day one. I've found some great steals over the years. For the online auctions--it's great because you can 'set-and-forget' your bids. You can place a max bid and it'll auto-bid for you which I find super convenient.
SELLING
When I was ready to sell a few items, the sales team was very attentive and helpful. They walked me through the entire process and it was very smooth. It was so much better than dealing with eBay or Craigslist on my own.
I highly recommend their services!