I think to be as accurate as possible, you're going to have to go through a few cycles with this program. First off, as Roy Johnson put it, compute a checksum on every file and compare them. Any duplicate checksums are truly identical files. Next, you should compare the file-names to find potential duplicates that may not be tagged or may be inaccurately tagged. Finally, compare the ID tags to find duplicate copies of songs that may have different filenames and be slightly different (different remixes or maybe just missing the last few seconds or different bit-rates, etc...).

Most importantly, I think you need to have your code output a file for a human to review, not do the deleting itself. If/when you complete it, I'd like to suggest that you post it on PM. I'm sure there are hundreds of others who could benefit from that!