Will your customers find out if you license your data?

Owners usually ask about customer privacy first, and some brokers make it the centre of their pitch. The biggest sale so far left customers out: Spirit Airlines' internal archive went on the block without passenger records, and the court named a consumer privacy ombudsman.

• Placeholders or codes. Every mention of a client such as "Henderson Roofing" turns into a code like "Client 0417", and buyers often show you a before-and-after sample.
• Scrubbing contact details. Phone numbers, emails and addresses are removed or masked.
• Excluding whole records. Folders, systems or customer accounts are left out entirely.

Read each buyer's own terms. On its partnership page, micro1 says it removes sensitive details before data is used anywhere else. Older versions of that wording were vaguer. The current written version is the one to rely on.

Removing a name is different from making a record anonymous. Per a Nature Communications paper, a mere 15 demographic facts let researchers pick out 99.98% of Americans. In a small town, an email about a particular job can point to one customer even without a name.

• Exclude your most sensitive customers' folders outright
• Review cleaned samples yourself before release
• Get de-identification standards written into the contract

You may prefer to tell important clients yourself before word gets out. Contracts with customers, your privacy policy and local law may also require notice or consent. Check all three with your lawyer.