I can comment on one of these sales as I recently purchased a Cortese that was listed here. The seller had bought the Cortese back in August, waited 4 or 5 months for delivery, then spent some time comparing it to another (much more expensive) preamp in his system. He decided he liked the other one a little better and listed the Cortese here. I was happy to pay close to full price to avoid the wait and import duties, so the deal worked out well for both of us. I haven't spent a lot of time with it yet so I'm hesitant to comment on the sound, but my initial impression is that it's every bit as good as this thread leads you to believe.
I think the long lead-time involved in getting Suprateks just naturally leads to a few new ones being listed here. People find something else, or relocate, or downsize their system, etc. before the Supratek shows up. I doubt this implies anything negative about the quality or value of the product.