How does CarGurus make a determination of being a one owner car?

I am in the process of corresponding with a seller and ran a Carfax which shows the first odometer reading as 17,343.  When I asked the seller this question they said "That's because they sold it overs seas so the original owner on the car wasnt recorded. So when I went to get the title transferred in my name, they had to put the previous owner as the start of the car. It's just a Germnay-America issue". I asked if there was more than one owner and the seller has not replied after 4 days.  Please let me know as I am really interested in the car but if the first 17K+ miles are unable to be verified to be accident free and no telling how many owners, I question why the listing shows one owner.