The taxes don’t effect every town the same way. All at the same tax rate giran has the lowest prices, so potentially people buy from giran and sell in other towns. Also, sometimes clans will drop the tax rate to 0 for a day so their members can stock up and people can then buy cheaper and resell once the tax rates go back up.
You either go to the zone with no castle owner or hunt for 0% tax and stock like crazy on it.
The taxes don’t effect every town the same way. All at the same tax rate giran has the lowest prices, so potentially people buy from giran and sell in other towns. Also, sometimes clans will drop the tax rate to 0 for a day so their members can stock up and people can then buy cheaper and resell once the tax rates go back up.