There are a lot of people out there to get you.  Scams are all over.  Sony puts stickers on the back of their products to keep everyone safe.  All of their playstation two's have one.  Before you go off to buy one, be sure to get pictures sent to you of the back warranty seal.  If it is not flat or appears scratched around or tampered with it has most likely been removed.  Some people can remove this without even ruining it.  This is when you check the auction, ask questions, and check feedback.  Also check around the endges to see if there are any pry marks or screws missing.

Here is a picture of what the seal looks like untampered with on the old PS2's


And here is a picture on the new Slim PS2's


The new ones appear to be thicker, larger, and more difficult to get off.  If you found this guide useful please say so and click yes it is very appreciated.