Last year, one of the members had a Damascus knife rust, I suggested he use Evaporust.
After trying all the other ideas presented in the thread, he still had rust on the blade.
He soaked it in Evaporust and it removed the remaining rust, didn't damage the blade or etching.
If you buy it, fill a glass with Evaporust, high enough to cover the blade to the frame/guard. Let it sit for a few hours to a whole day. Once the rust is gone, rinse it off with water, dry and apply some oil to the blade.
ETA: you might have to take the knife apart, and soak some of the other parts. I would think that AZCK would've cleaned it up, before offering it for sale.
If you clean the frame/scales to get the rust off. Use a q-tip to apply it directly to the spots. Don't soak them, as you could damage the carbon fiber.