You really can't get away without having a publicly accessible staging environment these days for remote clients. Or at least trying to use something like Vagrant to keep the environments as close together as possible. You can also have the client checkout the Vagrant environment with git then just pass your database to them when it's time to update.
Hosting companies like Pantheon include several environments like; staging, test, and live. While Cloud9 is a cloud based editor which means you could edit your code and share the results with a remote user in real-time.
WP-CLI does a really good job of giving you the ability to export / import and migrate databases.
And rsync will always be a great way to sync folders between servers.