Most "flexible" fares (particularly domestic) allow cancel for refund with no charges. There are some "flexible" fares that have charges for refunds, but they can generally be changed with no fees (only fare differences will be applied). It's all documented in the Penalties section of the fare rules which are available online after selecting flights and prior to purchase. The formatting on aa.com is not the most readable, but you can still figure it out if you know what to look for. Here's a "flexible" fare with AU origin with a fee for refund (fare basis code QLX5CRN3 for SYD-JFK). You just need to search for word "CHARGE" in Penalties section.

"CANCELLATIONS ANY TIME CHARGE AUD 500.00 FOR CANCEL/REFUND. "