Many times I personally ran into this problem where a file sent to me (by known person) does not open even though it has some extension type say Bombay.mp3. To root out all those problems here is useful tip from KrazyDad. He uses Hexdump to analyze the file type.

Here is the mapping

File Type – HEX DUMP
MP3 – ID3
WAV – RIFF

A Field Guide to Files via kwout