Why won't the Guide leave?

As of the latest update (1.1), there is an NPC UI that allows you to assign living spaces, as well as query a room to see if it is suitable, or why it isn't.

When I want to move an NPC to a new house, I do this:

1. Create the new house and make sure it is the ONLY place that has the comfort items required for a house (Bed, Light source, etc.)
2. Remove the bed, lights, chairs, etc. from the NPCs current house.
3. Get the NPC stuck in a hole so that a) the NPC cannot leave and b) lava cannot flow out (you can see where this is going :P )
4. Get a bucket of lava and dump it in the hole
5. The NPC will die and when they come back they should be in their new house

To get rid of the lava after that, you can turn it into obsidian.

When their current home becomes unsuitable, the NPCs try to find another home.

This generally involves a teleport. I'm not sure whether they can actually move into a new home by walking to it, but even so, they're not very good at navigating terrain. 3 block drops and jumps are all they can manage.

For obvious reasons, they won't teleport if you're looking at them. Leave them alone for a bit and they should move.