How to Validate for File Completeness after MGET

Hi All,

I need to connect to an FTP site using sFTP.
At any time of the day there could be .txt files dropped there.
I have a job on the scheduler that will run at intervals to check for .txt
files and transfer them to the IFS.

My question is how to validate that the MGET only transferred files that
were complete.
I assume that the MGET will grab files that may be in the process of being
created.
It would be great if that assumption is wrong!

How do I know files transferred with MGET are complete files?
I cannot dictate any changes to what is being dropped by our partner.

Thanks in advance for any info!
- Steve