I am looking at a couple of second hand Mac-book Air's and was wanting suggestions as to making sure I don't get locked out of it later if I did a re-install. Or any other possible security issues. Any help would be appreciated.
try to boot into the option menu, power on & press and hold the options key
If it boots up without asking a password, the efi password should be disabled.
You could also try options boot into a external drive. Once in osx, make sure find my is shut off...if enabled, the owner needs to use their password to disable it and ask them to remove the air from their itunes/icloud account