@chodhry, When your customers want a link you can generate a link form the “Admin Functions” of the WP eStore plugin.
The reason I don’t want to make it so you can have a link to the product that never expires (essentially a hard link) is cause people can take that and post it on forums and stuff and that jeopardize the security. Also don’t forget when you place a hard link on a page bots can pick it up.