Why don't the Overview figures match the Statistics?

Check the mode (daily or monthly) and the date. The Overview shows one day or one month; statistics usually cover a longer period.

A professional can't see the Accounting block. Why?

They need the Financial data permission. You can turn it on in their panel permissions.

How do I keep a test client out of the figures?

Open their file, go to the Profile tab and, in the Advanced block, tick Exclude from reports.

When does a client count as a drop-out?

When they go longer without renewing than your Time without renewing to count as a drop-out, in Advanced center settings.