Hi Ben.
Now more than ever Google is focusing on Brands rather than standard "keyword rich" websites.
Brands offer trust more than anything and is by far the best way to go if you plan on building a long lasting online business...
"Budget Car Rental" is a real brand, but then its also a money making term. Google has clearly recognised the term as a brand which is great and if your client can do the same, then no harm done.
It gets manipulative when your brand is "ABC car rental" and your website is "Budget car rental.com"
The only reason exact match domains are still ranking I presume is because Google is still tied up in identifying which are brands, and which are there solely for ranking benefits. Google's not stupid and things are changing fast.
I guess the best way to explain it to your client is to say:
For short term ranks with no guaranteeing on future success, then choose a URL with the sole objective of manipulating Google into ranking you well.
Or
Choose a brand name and built trust that will last for years to come.
If they choose to go the manipulative route, then at least you have done all you can to educate them leaving you with a clean conscious for when they regret the decision made.
Just my 2c worth...
Greg