Catherine,
Moz's local expert, Miriam Ellis, gave the following answer to a similar question a while ago and it goes straight to the point. If the client can't sincerely answer yes to the following questions then they would be putting their existing local listing in jeopardy of being penalized or merged with another listing.
1) Does the business have a unique, dedicated physical address (not a virtual address, P.O. Box or shared address)?
2) Does the business have a unique, dedicated local phone number in the city of location (not an 800 number, not a call tracking number, not a shared number)
3) Does the business have in-person transactions with its customers, either at its own location (like a restaurant) or at the customers' locations (like a plumber)?
If the business does not meet any one of these 3 criteria, it does not qualify for local inclusion. I don't know where your client is at on points 2 and 3, but if they can't say yes to point one, Local SEO will be nothing but problematic for them. Here's why:
If 2 or more businesses share an address, suite address or phone number (or even if their names are too similar), Google will frequently merge the business details of the listings. This means that Joe the Barber can end up with Jim the Plumber's business name, phone number or reviews showing up on his listing. Merging is one of the most difficult issues to deal with in Local, and one to be avoided at all costs.
Here is a Google help file on this issue: http://support.google.com/places/bin/answer.py?hl=en&answer=175290