I have purchased there a few times. They use the US postal system for final delivery. I have never been hit with duties.
Pediwear doesn't always use postal service so when ordering, be sure to specifically request it.
Got a nasty surprise when they used UPS once.
@bustert there's a whole thread devoted to customs and duty charges in the SW&D forum I think.
Basically, for shoes, duty will be about 8.5% plus possible brokerage fee of around $25 depending upon courier and service.
DHL and Fedex will bill after delivery. UPS and USPS collect at delivery.
USPS there's no brokerage fee and chances of getting hit with any charges are very low.