I copied this from another guide and updated it.

Don't get taken advantage of. For those of us who are in the market to by an EFI tuner, and trying to save some money, I HAVE A VERY, VERY IMPORTANT piece of advice for you. Most EFI tuner can be a very worth-while investment. However, there are somethings you NEED TO KNOW before purchasing.

The EFI tuner has four components:

1. the ECM cable

2. the tuner itself

3. the interface cable

4. the CD-ROM

HERE IS THE PROBLEM WITH BUYING A  TUNER ON eBay:

Most tuners have a memory interface, the new units will be packaged in a sealed unit.  The reason it is, is because the tuner needs to be registered for the software to work. To register it you must hook it up to a vehicle, so it can get the vehicle identification number or VIN to activate the tuner. This keeps someone from buying a unit and tuning all his buddies vehicles. That VIN number is the only thing that the tuner will respond to. So if you don't know the VIN number that it is married to, it will not work! If you do know the number it goes by the previously entered information. So it will not tune your vehicle at all.

SO if you see a tuner, and the tuner is out of the package DO NOT BUY IT!!!!!!!!!!!!!!!!!!

YOU WILL BE BUYING A USELESS PIECE OF EQUIPMENT!!!

You can call anything you want "new", that doesn't make it TRUE!!!

Some sellers are unaware of this, others are out to take advantage of people.

How do I know? I was one who got ripped off!

Can you save some money buying one on eBay? Yes, but do the homework. And remember the saying "you get what you pay for".

This covers all Harley-Davidson Flash Tuners, the DynoJet Flash tuners for autos and motorcycles and many other tuners that flash a new fuel map, timing map, or programs into your ECM.  I have been through this 3 times now from sellers that assured me that the tuner has NEVER been used.  DO NOT BELIEVE THEM!!!