Hello.  I am writing to share my experience, and hope that others can avoid making the same mistake I made. 

Many Sony Z700s on ebay look to be a great deal.  A pair of headphones that normally cost around $150-200 brand new for between $51-100.  Most people that buy these headphones really have no idea they have been duped.  There are a couple big differences I noticed with my fakes right away.

The Cord.  Sony uses a coiled cord, but are usually a flat black, and very stretchy.  The purpose of the cord is to allow flexability when moving around the dj booth/studio.  The fakes have a coiled cord, but are a shiny black and the cord is very tight, allowing very little movement before pulling the plug out of the mixer.

The Jack. The real Sony 700 headphones use gold plated, screw on 1/4 inch jacks.  The 1/4 inch jack screws onto the 1/8 inch jack to ensure proper connection for the headphones.  The fakes have gold plated pop on jacks.  This type of connection allows for the sound to cut in and out when using the 1/4 inch jack.  If you are only using the 1/8 inch jack, the sound will come out clean.

The Instructions/Manual. Sony has nice manuals and warranty information with their headphones.  The fakes only have a single sheet of paper with all the different languages.

The headphone bag.  Sony has had several bags for carrying their headphones, but most have been a nice, shiny, velvety material.  The fakes have a basic flat cloth bag.

The fakes do sound ok.  If you are only using the headphones for recreational use for a portable player, they probally are a decent pair of headphones for the price.  If you are using them for djing or remixing, or any type of studio work, I would avoid them.  The cords and jacks are not condusive to this type of work.  I purchased the fakes, and had to buy a new pair of phones.  I bought a pair of TAKSTAR off ebay, and they look similar in style to the Sony 700.  They sound better than the fakes, have the screw on jacks for better connections, and  come with to cords, a coiled and straight.  The cords are easily replaced, which is a bonus because cords usually wear out before the mechanics do.  I hope this little list serves you well.