Another thing I see a fair amount of is someone buys a property as a slight discount, rents it, but puts it on the sales market as well to try and see if anyone will bite at the higher price.
I can't say this strategy works particularly well but I do see it happen.
All that said their are successful flips that still occur. Buyers who are able to negotiate a below market deal thanks to a foreclosure or a seller in distress or developers who identify profitable ways to improve units like carving out a second bedroom or developing existing roof rights can flip at a profit.
Unit 309 was pulled off the market in October. Expect that it was either rented or will show up for sale again just in time for the spring market next year.
There is one bank owned listing in Back Bay right now (see link below). Worth a look if you are thinking about a flip.