If they hammer it, then check the MFD, it will tell you the top speed they went including the average speed. you could always tell them you'll check that before they set foot in it.
It will tell you the top speed they went?
Is that an option in the MFD?
It will certainly tell you the average speed which means nothing.
I went to Dundee and back at the weekend doing over 90 the vast majority of the way there & back and on occasion over the ton (I was late, honest your honour) but when I checked my average when I got back it told me it was 42mph!! Slowing down for average speed cameras, fixed cameras, traffic lights all bring the average down so doubt he would get much info after the delivery driver has delivered it.