I can think of a couple of ways to optimize this so that you don’t get duplicate client records, but they all involve script actions as part of the automation design. Until Airtable implements conditional logic and branching into the automation architecture, a script action is the only way to do this kind of advanced behavior. A script could search your client list for the client that is tied to a given product that led to a conversion. If that client is found, it links to the existing client record; otherwise it creates and links to a new client record.
Script actions in automations require that your base be in a Pro-plan workspace or higher. If your base meets that criteria but you’re not comfortable writing scripts, and you have a budget to cover development, message me and we can talk in more detail.