There still appears to be lots of fake shure microphones out there, and I've just bought one (beta 58A)! fortunately I have several genuine shure mics to use as comparisons, the trouble is that buying on ebay you don't get to see and feel it until you've been and paid for it, and its all a bit late then. I have read several articles on what to look for and they are most helpful, but to be honest visually these mics can look really good and if you do not have anything to compare with, they can appear genuine. I handle shure mic's all the time and as soon as I picked it up I knew it was fake because of the weight, this is the first clue. Check on shure's website for the weight of the mic you are interested in and compare it, mine was 3oz lighter! The next thing I noticed was the connector details, the pins should be numbered 1,2 and 3 and you should be able to see a small metal locating bar opposite the no2 pin, above the no2 pin you will see shure logo. Mine has numbered pins but has no metal bar and shure is written opposite no2 pin rather than above it. Unscrew the mesh top and on on the beta mics there will be a yellow and green wire visable on mine they are black and were covered with a yellow tape. There should be a case with the mic with an enbossed shure logo.
I'm sure that the detail on the fakes will vary and they will be getting better at making them so the best advice is to buy a genuine one from a dealer. If you are buying one from ebay then ask to confirm details and pay using paypal so at least you should be have some comeback, never ever buy one being stated as new at way below retail price. Having said that I did buy a beta 58a in very good condition but the seller had taken lengths to photograph and describe the item accurately, of course people can equally lie as in my latter purchase- proceed with much care!!