[staggolee]

Well the first decision you should make is which company you want to tune your car. You can buy a preowned tuner, but you have to make sure your tuning company (such as brenspeed or bamachips) uses a software that is supported by that tuner. I just did a quick check andboth brenspeed and bama sell and support the SCT so purchasing one of those off of craigslist would be fine. The difference between buying one that is locked or unlocked is an unlocked one is ready to be retuned. if you buy one that is locked then you will have to call tech support, get a return authorization, and pay an unlocking fee of $150. Don't buy a used tuner and use the same tune as the previous owner, purchase a new tune specific for your car from a professional tuner (like the previous mentioned ones). It's not that expensive for just one tune and they are also sold in bundles. The gains you will get from a tune depend on what kind of octane you are getting tuned for and the type of tune (race, torque, performance...), but I believe an average of 15 horsepower should be expected. I hope that wasn't too long winded and if you have any more questions feel free to ask here or even email a tuning company directly, although i know they are very busy lately since it's "tuning season" so it may take some time to get a response