Drone video high definition file recordings are on the drone SD card, not on the controller. Make sure you copy all new video files to your computer after each flight. Only very low resolution video files are on the controler.
You should have asked for battery details, including the number of charge cycles on each an the date of original purchase. If the details aren't satisfactory, then your risk goes up and your offer price should drop to match your increased risk.
The receipt seems to be rather generic and non-descript and doesn't even mention batteries, so not much to go on. "Minimal wear" is rather useless for any electronic equipment. The seller should have written out details, not used the generic...