Before buying your new or old computer, the most notable thing is why - and for what purpose you need the computer Many people just buy high-spec computers for the sake of mood (the truth is true). Your work is just for word processing software and you have bought i7 processor and 16gb RAM computer! what for? Kenona will never work for you, this is nothing but a waste of good money.
Specification
When the first point is your requirement, then you must pay special attention to your laptop speaker. Of course, the software you need to have the ability to run on that laptop. Are you trying to make gaming, or are you trying to edit audio video, or are you buying a laptop to play media? In that case, the CPU, GPU, RAM, and storage should be kept in mind.
Physical checkup
After you need your hardware and hardware specification, you will have to physically check the old laptop, say medical checkup. First of all, check whether the laptop's body is fine, whether it is broken in the frame or not.
Checking the screen after checking the body is the most important checkup. Take a look at whether the screen is blurred or fluttering, check the brightness level, and see if there is a bad pixel on the screen. I would recommend watching the video viewing angle.