Transfering another file is a good idea IF you put the verifiable information into it about the main file you were sending. On a ftp from one UNIX system to another, I put the output of ls -s mymainfile.dat into filesize.dat. Then on the receiving side, the cron job that runs waits for filesize.dat to start processing (this also insures that the main file is completed since it went first).
It gets the information on the size of the file and compares it.

You could (if going from UNIX to UNIX) also use the sum command.