FTP Download - How to check File exists

What is the cleanest way to :
 
1) Check if a file exists on an FTP site.
2) Sample the size of that ftp file (3) times to ensure the file is ready for downloading.
 
We have some classes doing this already but they are using WebRequestMethods.Ftp.ListDirectoryDetails and then searching there in if file exists.  I am hoping there are some clean ways to do this.
 
Thanks in advance
 
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