I found this useful thread recently,you can distinguish the DSTTi Genuine from the fake one.This is the only way to be 100% sure you have a genuine DSTTi or not.Because of the last 3DS firmware for DSTTi,and all the problems that some people have with,the author decided to take some picture by himself..and these are the pictures. This is the only one "GENUINE" GREEN PCB DSTTi This is the "GENUINE" RED PCB DSTTi This is a fake Green PCB DSTTi This is a fake RED PCB DSTTi (1.4) Genuine DSTTi dont have any glue, so you can open it easily with your fingernail
Buying a quality DSTT is becoming more and more difficult these days, so we should to find the right retailer.