WOW!!!
I want it!!!!! LOL
Obviously they are leaving the price up to you.
Are they having a bidding on it, or is it just going to whoever makes the first cash offer?
If they paid $1200, then I would offer at least $600.
A "trick" of buying through a method such as this, is to literally have the cash in your hand when you make the offer. People rarely say no to a wad of cash staring them in the face.
I looked on Ebay, and the cheapest mixer of this type (used) was listed for $350, but it was not a Boxer brand. The cheapest Boxer brand I found was $900, brand new, for the one you have pictured. So I think $600 is a good start.
If they say thats too little, add a $20 to the stack. If they keep saying no, keep adding a $20 until you get to your spending limit. --- thats just a suggestion
Let us know what happens.