When using Add-PackageSource, there is no verification of whether the source actually exists. It just adds the source with no questions asked and you won't know until you attempt to find/install a package that the path is not valid.
Add-PackageSource -Name Fail -Location http://this.willnotwork.com/keeptrying -Provider Chocolatey
Even though this is obviously wrong, it is still added and appears in the list of sources when using Get-Packagesource.
Some sort of checking, be it using Invoke-WebRequest (if url; otherwise Test-Path for folder) or some other approach to verify the validity of the location would help to ensure that the proper package sources are being added to the list of available sources.