Factory reset
Won’t allow me to factory reset my computer for sale
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What is the exact model of your laptop? You can get this information by clicking on the Apple menu and selecting "About this Mac" or by entering your serial number here:
https://checkcoverage.apple.com/
What version of macOS is currently installed?
If macOS 10.12.6+ has been installed on this laptop at some point in its life, then you can boot into Internet Recovery Mode using Command + Option + R to install a later version of macOS which doesn't have the same issues as the online Lion installer seems to have.
https://support.apple.com/kb/HT204904
If you can boot the Mac or you access to another Mac which can run an OS the old laptop can run, then you can create a bootable macOS USB installer using these instructions (also includes links to the installers for macOS 10.11+):
https://support.apple.com/en-us/HT201372
If you Mac shipped with DVDs, then you can use the DVD to install macOS.