Two customer records look like the same person. What do I do?

Two records merge on their own when two real email addresses agree, or when neither has an email and they come from two different systems with one phone number and names that do not disagree. A shared phone alone is never enough: two people saved separately in the same system, or two different names, stay two customers, because spouses and offices share phones too. Anything less certain is a question for you. "Same person" merges the records and moves their payments, their open invoices, quotes, jobs, visits, schedules, notes and addresses onto one — a paid invoice stays where it was issued and still shows on the customer's page — and Undo puts back exactly what moved; "different people" is remembered so the pair is never suggested again. Suppliers get the same treatment on the Expenses page.