I have noticed an increase in fake Oakleys that Ebay is allowing to be sold.  It really irritates me, especially when Ebay does nothing to uphold their policy.  Here are some tips on avoiding being ripped off.  I am not affilitated with Oakley in any way, but I have worn and collected them for nearly 15 years. 

• Just because they come with a box and a bag doesn't mean they are real.
• Just because they don't come with a bag doesn't mean they aren't real.
• Many Oakleys are auctioned off and sold every day, so don't get impatient and buy something you aren't sure about. 
• On a search engine, type in fake or replica Oakelys and view what they have.  Check more than just one site.  You can see the same picture and same junk sunglasses that these sites are offering.  In many cases the sellers are using the exact picture.  Common for fake Minutes, Radars, Gascans, M Frames, Twentys, Eye Jackets, Oil Rigs and probably more.
• Go to the Oakley website or O-review to view and compare, especially lens color.  Many fakes have lens colors that Oakley never produced.  Often you can do a search and type in the sunglasses model and you can bring up pictures of the retired models.  Doing 20 minutes of research is better than throwing money down the drain.
• If they are a popular style and they only have 1 or 2 bids towards the end of the auction, chances are many people spotted them as fakes so they aren't being bid on. 
• On M frames, check the lens shape and color.  If it looks cheap, it probably is cheap.
• Wire frames, the nose pieces are replaceable.  Ask for a picture of the nose pieces.  The rubbers can pop in and out for replacing, so examine the picture to make sure. 
• Most plastic frames, excluding the very first edition of Eye Jackets don't have the 'R' trademard logo after Oakley.  Be sure to examine the OAKLEY across the bridge.  If it doesn't look centered and correct, they are probably fake.  M frames and Radar lenses have the 'R' on them. 
• Oakley doesn't put stickers on the lenses.  Some of the newer styles have a sticker smaller than a Cheerio on them, but that is it.  No UV Protection sticker or any other bs.  Ask yourself, why would they put a large sticker on expensive lenses?  They wouldn't.
• Even if you buy a pair and you question their authenticity, you can't always trust an Oakley dealer at your local mall.  Most of them that I have encountered don't know a Straight Jacket from an Eye Jacket.  Oakley Vault stores you are probably safe with asking their opinion.  When in doubt, you can always send them to Oakley.
• Check the feedback and don't just look for negatives.  Read the feedback because sometimes the seller still recieves positive or neutral feedback if they gave a refund.  If they have been accused more than once for selling fakes, they probably are selling fakes. 
• Not every person selling fakes knows they are fake, but the majority probably do.  They aren't going to come out and tell you, so beware. 
• Use Paypal so that if they are fake the seller is more likely to refund your money.
• Hong Kong, Thailand, China......probably fake.
• If they look like cheap junk you could get at the gas station, they probably are.