True bad ROMs will have a "[b1]" *NOT* "[f1]" or "[t1]". "[f1]" is a "fixed" ROM, which means that it was converted from PAL to NTSC, vice versa and/or had the anti-copy protection cracked. An example would be Jet Force Gemini. "[t1]" means the ROM was hacked to include a trainer.
Also, a ROM...