Greetings from inside the SEOigloo,
I’m sure you’ve seen this for your own local business or with your client’s listings. I’d like to provide an example of shifting results between the 3-pack and internal Google Maps results.
We launched a website for our client a couple of months ago who offers licensed elder care services. As you can see below, the site is already doing immensely well with an indented listing at positions 1-2 in organic for the search term ‘elder care home napa ca’, though it is not yet appearing in the 3-pack.

Because, like so many business owners, my client is incredibly busy, it took a couple of months for us to coordinate registering with Google’s Local Business Center. I completed this task last night, and am amazed to see that he’s already made it into the A-J rank inside Maps at the C position, as shown below:

That’s the fastest induction into Maps we’ve ever seen, but what I want to point out here is that, while my client is doing well within Maps, he is not in the 3-pack, despite his authoritative indented organic listing. You’ll note from the example that the rankings between the 2 interfaces have been switched about in several ways for the other businesses, too.
Why does this happen?
Greg Sterling had some great data on his site a couple of weeks ago regarding the way in which Yahoo! local values local listings, but what is Google doing?
To my way of thinking, doing well in either the 3-pack or 10-pack has most value simply because of the percentage of organic to Maps users. That’s obvious.
I hope folks will share their theories about this and I thought this was a useful example because:
1) If organic is influencing the 3&10-packs, why wouldn’t a top ranked site with an indented listing be the natural choice for inclusion in the pack?
2) If Google reorders things once a user clicks the ‘more’ link in the pack, are they doing this because they figure the user didn’t see what he wanted in the 3 or 10 sites shown and is attempting to get more information or refine his query?
Because the local listing just got validated, in this case, I’ll need to keep checking to see if it will, in fact, pop into the 3-pack soon. It seems very random, if you look closely at the first image, that the 3 pack is pulling only 2 sites from Napa and the 3rd from miles away in a little town called Glen Ellen. My client offers Google a more local result for this search phrase, and I hope Google will take note of that shortly.
I’d value any and all thoughts on this.