Returns the channel commissions that currently apply to the listing, after resolving the listing level configuration.

If the listing is configured to use account settings (levelEntityType = ACCOUNT), account-level commissions are returned. If configured for listing settings (UNIT_TYPE), listing-level commissions are returned. Each item includes the effective levelEntityType so clients can see which level was used. If unitTypeId is a sub-unit, it is resolved to the parent unit type before lookup (sub-units are not rejected with 400 on this path).