Question: How can I determine that a particular file (which may or may not have an ".mp3" file extension) is in fact an MP3 file? I wish to do this in C#.

Answer: 
1. using file extension is not reliable.
2. the best libary you can use is <https://github.com/mono/taglib-sharp> it detects most of the common file types. maybe you just want mp3, so you can extract any mp3 related class.
3. a simpler library you can use is <https://github.com/judwhite/IdSharp>
```
string[] filePath = Directory.GetFiles(fbdialog.SelectedPath.ToString(),".mp3", 
                                       SearchOption.AllDirectories);

foreach (string str in filePath)
{
    MessageBox.Show("It's mp3 file");
}

```