This should only happen when you choose UPS or Fedex lowest cost and quality shipping option. I believe this only happens with international shipping, only recall this happening with cheap items sent from ebay international sellers.
Actually, its not advantageous to use postal services for international shipping, just the opposite. Fedex, UPS and DHL act as brokers for these shipments, speeds up customs process. I've had terrible experiences with postal services, packages nearly always in customs for at least a few days, sometimes for weeks, even months. I never ship international with USPS, and always try to upgrade service on shipments to me.