As a caveat, while I myself would generally only buy a '57 new from a reputable vendor at this point, I'll also suggest that if someone has a '57 in their possession, some of the "experts" on the internet have posted things that suggest certain features indicate a fake mic, but do not. I was convinced that I had a fake at one point, and threw the mic in a box for about 10 years. I looked again later, with a more critical eye, and some of the things that had been suggested as indicating a fake were in fact reflected in pictures of actual products on Shure's website. Things like the number of holes near the XLR connector and the specifics of the typeface on the label have actually changed over time. Looking at the wire colors and for the presence of the transformer are overall better indicators.
Also, because I'm mildly contrary, I'll say that I own an e609 and an e906, but I find '57s more useful in many situations.
...The e609 actually gets pressed into service for weird, effected vocals sometimes.