How much should a dive trip deposit be?

It varies by trip. What matters is that the amount and what it covers are stated before you pay, not discovered after.

Is a non-refundable deposit a red flag?

Not by itself. Part of a deposit is often genuinely spent on commitments in your name. It becomes a problem only when the non-refundable part was never disclosed in writing.

What happens to my deposit if the operator cancels the trip?

That is a different situation from you cancelling, and the trip's terms cover it. It is one more reason to read the terms before you pay.

What Your Dive Trip Deposit Actually Does

A dive trip deposit does two jobs: it holds your spot while the operator commits real money on your behalf (boat space, rooms, permits), and it covers those commitments if you cancel late. What varies is whether you ever saw the terms. Openwater shows the deposit, the final payment date and the cancellation terms on the trip before you pay anything.