Flipping rares is VERY profitable. I just started doing this, flipping my own mask, and each flip would yield 2-5m profit. Each flip took half an hour or so though. IF i had a cash pile of 1b +, flipping 8-10 rares at a time, each flip being 2-5m every 30 mins... Jesus. (18-45m per hour based on these calculations) ofcourse I would have to do 100x more work with more than one item flipping at once, so most likely it would not be as profitable.
Flipping new items is 10x more profitable.
Now that the secret is over, I would buy "Ward of Subjection" for 10-12m and re-sell them for 15-25m. This update was very profitable!!
BTW - dont try the ward of sub' flip anymore, it DOES NOT work anymore, because the news items are stabilizing.
Unstable new items are the best to flip! (on the street works better than GE)
In all, 10 hours (aprox) of flipping these items has profited about 80-100m. (8-10m per hour!)
Cant wait till next update!!!