All parcels are sent Delivered Duty Unpaid (DDU) which means that you should receive no further import tax fees as long as the value of your parcel does not exceed the parcel value you stated when being sent. If upon arrival, your parcel's value is found to exceed that the sender will incur any relevant import tax fees or face their parcel being rejected.
The Ship24 fixed prices are designed to cover the tax threshold of destination countries so that the receiver will not pay any delivery duty tax/import tax. For exceptions, please check with your parcel's destination country as Ship24 is not responsible for wrongly valued parcel valuations resulting in import tax fees.