I think if you're 'importing' exotic leathers, definitely use a courier (Fedex, UPS etc). They at least notify you, and try to move the stuff through customs. USPS just doesn't cut it. The only problem is that couriers charge you for their clearance services, and you'll definitely be slapped with heavy duties.
Paid 180 USD worth of duties on my Lobb's from England. Shitty.