Q: wipe clean

What to do before selling or giving away your Mac - Apple Support

If the Mac does not have Lion or later you need and installation DVD.

What model Mac?

That is a 2010 MacBook Pro that does not have Internet Recovery.

First try booting to Recovery

https://support.apple.com/en-us/HT201314

Then format/erase the HD and try to reinstall OSX via Recovery. It is ask for your Apple ID and when you enter it says the action can't be completed then shutdown and boot from DVD (Insert DVDand boot with the C key depressed) and install OSX for disk and then update as necessary.

If you can reinstall OSX via Recovery then do that.

You just inherited a Mac, you don't have access to passwords. I don't want to sound like a jerk here, but if you got a computer from someone, wouldn't you want to know how to use it and what would be on it, including passwords? The first thing you probably want to do is ask for the passwords. If it's now your machine, the person who willingly gave it to you should have no problem giving you full access to that computer.

Not that I'm trying to point fingers here, but I hear quite a bit about stolen computers and having to replace their stuff because someone thought it would be great to take another person's property.

Not all software is transferable to the new owner, especially software download, this includes Apps purchased from the Mac App Store.  The Mac Store purchased apps are locked to the Apple ID used to originally purchase them.

The seller should have done what Apple specified in the link in my first reply