Hi Bede,
I confess, I don't have any strong direct experience with Yodel, but, from what I've read in the past, they do appear to have a rather direct relationship with Google and there have been some complaints in regards to their creating new Google+ Local listings (some even with taboo call tracking numbers - uh-oh!). *Remember, I'm just repeating what I've read from other Local SEOs - not what I've experienced first-hand.
Your question made me recall a thread I'd read months ago at Linda Buquet's Local Search Forum. I managed to find it again and I think it will be helpful to you:
http://localsearchforum.catalystemarketing.com/google-places-help-support/4181-yodel-claims-clients-places-listing-but-dashboard.html
What's surprising to me, honestly, is how little overall documentation there appears to be from third party sources about Yodel's process, Bede. Here's an old thread from Mike Blumenthal's saved version of the old Google Local Business Help Forum:
http://places.blumenthals.com/thread3eeb.html
And there is stuff from Yodle like this:
http://www.yodledentalmarketing.com/blog/post/claim-local-search-listings/
But the main thing that I recall about this particularly company was a rash of complaints years ago that their sales reps were somehow convincing business owners that they were calling from Google in regards to AdWords. Do you remember that?
At any rate, my take on this is that there just isn't a ton of 3rd party documentation from the Local SEO community about this company, but that your client may well have had his listing claimed by Yodel, given all of the above. I hope my reply is at least somewhat helpful!