You can just deactivate your PS4 under settings, playstation network per this article
https://www.playstation.com/en-gb/g...ion/how-to-deactivate-a-playstation-4-system/
After that you can just do a quick re-initialization of the PS4 to erase the saves under system, then go through setup and let it create User1 as a login to the PS4, that way when you take it in they can quickly verify its working instead of having to spend 10 mins going through setup. Shouldn't take more than 5-10 mins.
Even if you forget to deactivate your PS4, like I did, you can deactivate ALL your playstations once every 6 months on the Sony website. I had to do that since I forgot to deactivate my PS4 and couldn't activate my PS4 Pro as my primary system until the old one was deactivated.