Customer Match.

Many companies hold valuable lists: existing customers, newsletter subscribers, prospects from trade fairs or enquiries. With Customer Match these contacts can be used as an audience in Google Ads. The data is hashed with SHA-256 before or during upload, Google matches the hash values against signed-in Google accounts and builds a list from them. Google never shows advertisers which people were matched, only the approximate audience size.

The uses are varied. You can address existing customers with a follow-up offer, such as a service after purchase. Conversely you can exclude them from new-customer campaigns so no budget goes on people who are already customers. In Search, bids can be adjusted for known contacts, and in Performance Max customer lists serve as a signal the system orients itself by. For Smart Bidding and new customer acquisition, a list can help distinguish existing buyers from new ones.

Google ties use to requirements, including a good policy history for the account, and the list must be large enough to be served; small lists therefore often have no effect. Legally, what matters is that the contacts know their data is used for such advertising purposes. A list from quotes is not automatically cleared for advertising. The privacy policy must describe the use and, depending on the situation, consent is needed; in Switzerland the principles of the Data Protection Act apply, and for contacts from the EU the GDPR as well.

The counterpart at Meta is called Custom Audiences, at LinkedIn Matched Audiences. The principle is the same: upload a hashed list, the platform matches it, an audience is created. For B2B LinkedIn Ads, company and contact lists are particularly interesting because they enable account-based marketing. Every use requires a well-maintained data foundation: duplicate, outdated or badly formatted entries reduce the match rate on any platform.