They may or may not give you actual client names, but they should be able to give some high level information about similar Google Ads accounts they’ve managed. To get the best value from your budget, be sure that your agency can handle your needs and requirements.
Not all Google Ads strategies are created equal. Some are much more advanced than others, some have a larger team to handle larger companies, and some offer to integrate your PPC advertising into a fully functional inbound marketing campaign.