My experience had nothing to do with brand new Shure Microphones as there are plenty of good guides here.  My advice is to watch out for the used auctions with descriptions like Hardly Used or Used Once for a recording project in my home studio.  Do your research.  Descriptions like this may not mean there is anything wrong but they may be a warning so check the seller out to be certain.  Once I checked out the history of one seller, I found 45 of the identically described microphones over the last 30 days.  Who in the world goes through microphones like that?  Unfortunately I found out once I received one and compared it to one I already owned and could easily spot the difference.  At least he did give me a refund once I returned it.  Used Shure Microphones can be as bad as new ones but perhaps less suspicious.  I have reported this to eBay but as of yet, the seller is still selling.