I don't know this seller, but if i remember correctly, i've seen S7's on this forum going for around $400 (in BTC).
Given that the shipping is free, and you get a PSU, it might be a reasonable deal.
Don't forget: maybe the shipping is free, the customs charges might actually cost rather much. I know in some countries, those charges go up to 50 + 20% (or even more)
That's actually the thing I'm worried about right now : the customs.
There are only 2 countries in the world where UPS, FEDEX, DHL, guarantee the delivery only until the customs, after that they removes any responsibility ( the first one is North Korea
)If you ask someone from my country to describe our customs using one word, they'll directly choose "thief"
, they're reputed for stealing everything especially electronics stuff, they're basically making their own laws, sometime they'll charge you 75% for a graphic card and sometime they'll charge you 0% for a PS3 (both are true stories), I hope I'll not have problems with them,I think I might ask the vendor to fake the price on the invoice to avoid those thief, but I know that they do a research with the item reference on google and the first price they see on ebay or amazon they'll make it the original price 
.