Okay, I'm using a lot of my own trade as proof for this one. Vintage Sandviches sell in a very weird way. NO ONE offers for 0.66 ref directly, and since outpost don't show sold items, so its hard to find out if they were sold for 0.66. But I can tell you that its possible to sell at 0.66 ref. Most of the trades at Outpost which is selling the sandvich at 0.66 ref didn't exactly sold them off. But when I did an experiment on my own, the results were interesting.

Okay, to elaborate further on my experiment, what i did was, I bought vintage sandviches for 0.33 ref and then try to sell them for 0.66 ref. At first, I was not convinced that I could sell them for that price, but the results turn out otherwise. In just one week (this week), I sold off 6 vintage sandvichs by just posting on outpost. Time posted ranges from a few hours to 1-3 days. My own proof + a few side proof are below:

Selling for 0.33 ref:

http://www.tf2outpost.com/trade/8449697

many more trades selling and sold for this price, isn't necessary to prove that as this is already the current price.

Being offered 0.33 ref:

http://www.tf2outpost.com/trade/8305169

http://www.tf2outpost.com/trade/8390787

Selling for 0.55 ref:

http://www.tf2outpost.com/trade/8448531 (7 hours ago)

Selling for 0.66 ref:

http://www.tf2outpost.com/trade/8450242

http://www.tf2outpost.com/trade/8431150

http://www.tf2outpost.com/trade/7807896 (being offered 2 rec, but trade didn't go through)

http://www.tf2outpost.com/trade/7942444 (same guy as the link above, with an offer that didn't go through)

Sold for 0.66 ref (my own trade, within a period of 1 week):

http://imgur.com/2CgnIuL,y0eTj0C,fQ3OK2b,8HIoqRI,0LCmtkR,Qf0ZlGA#0

http://imgur.com/2CgnIuL,y0eTj0C,fQ3OK2b,8HIoqRI,0LCmtkR,Qf0ZlGA#1

http://imgur.com/2CgnIuL,y0eTj0C,fQ3OK2b,8HIoqRI,0LCmtkR,Qf0ZlGA#2

http://imgur.com/2CgnIuL,y0eTj0C,fQ3OK2b,8HIoqRI,0LCmtkR,Qf0ZlGA#3

http://imgur.com/2CgnIuL,y0eTj0C,fQ3OK2b,8HIoqRI,0LCmtkR,Qf0ZlGA#4

http://imgur.com/2CgnIuL,y0eTj0C,fQ3OK2b,8HIoqRI,0LCmtkR,Qf0ZlGA#5

here's my trade (you can click on the sandvich to see current owner):

http://www.tf2outpost.com/trade/8449698

http://www.tf2outpost.com/trade/8430100

Let me know what you guys think about it. The other proofs besides mine isn't really very convincing. I just want to stress on the point that this item do sell at 0.66 ref.