Getting O/S for "Cleaned" Used Macbook

You can try booting into Internet Recovery Mode using Command + Option + R. If macOS 10.12.6 or 10.13 was previously installed, then it should boot into the online macOS 10.13 installer (sometimes it will instead boot to an old macOS installer instead like macOS 10.7 or 10.8).

If you have access to another Mac that is compatible with macOS 10.11 or 10.13, then you can create a bootable macOS USB installer:

https://support.apple.com/en-us/HT201372

Otherwise you would need to purchase an original macOS 10.6.1 Snow Leopard DVD (disc with a gray label with your exact model laptop listed on the disc). A DVD for any other model will not work. I don't know if Apple sold a retail copy of macOS 10.6.X that had a revision number higher than 10.6.1 or not, but if so then that may work as well. You will most likely have to find a copy on eBay since Apple no longer sells the DVDs.

You will need to properly partition and format the drive before installing macOS on it. How you do this depends on what version of macOS you are installing:

For macOS 10.11 to 10.13:

https://support.apple.com/guide/disk-utility/erase-and-reformat-a-storage-device-dskutl14079/mac

For macOS 10.6 to 10.10:

https://www.owcdigital.com/assets/support/support-formatting-and-migration/Mac_Formatting_6-10.pdf

With macOS 10.13 Disk Utility hides the physical drive from view so you must click on "View" within Disk Utility and select "Show All Devices" so that the physical drive appears on the left pane of Disk Utility. You must select the physical drive to erase.

If you are using macOS 10.6 to 10.10, then you need to select the physical drive and use the partition tab.

The links I provided in the previous post should show how to do either option.

Also make sure you are selecting the internal drive and not the installer disk/volume. If you don't see the physical drive, then it means the drive may have failed or perhaps there is no internal drive installed.

From the installer you can launch the Terminal app from the Utilities menu and run the following command (press the "Return" key at the end of the line to execute the command):

diskutil  list  internal

FYI, First Aid only checks the integrity of the file system and not the files themselves. All it takes is for one bit to be flipped in a system file for macOS not to work or boot properly. Whenever I check the integrity of a USB stick almost always I find at least one bit getting flipped.

If you have the white MacBook (late 2009) unibody laptop, then you need to use the original DVDs that shipped with your laptop. If Apple made a retail version of the Snow Leopard DVD above macOS version 10.6.2 (I don't know if they did), then that would also work, but the original retail Snow Leopard 10.6 DVD won't work on your laptop. Be very careful to buy the correct DVD if you don't have the original DVD which shipped with the laptop from the factory.

FYI, a white unibody MacBook (late 2009) model can run up to macOS 10.13.

The circle with a line through it means that version of macOS isn't compatible with your Mac or perhaps the OS on the drive is bad (corrupt or damaged).

https://support.apple.com/en-us/HT210901

If you followed the official instructions in the Apple article I linked to create your bootable macOS 10.11 USB installer, then perhaps the USB stick is bad. Try using another USB stick since the quality of USB sticks is extremely poor and the USB stick may have corrupted the installer.

Your Mac is too old to have the Startup Security Utility.