We have customers that do it both ways. Many accounting/bookkeeping firms create a single SmartVault account for managing all of their clients; some prefer to let the client(s) purchase SmartVault for themselves, and invite the CPA as a user.
This decision typically boils down to a few factors, including who wants to own the billing relationship with SmartVault, who wants to administer the account, and whether or not the accountant wants to use SmartVault as a client portal for all of their clients.