I order stuff from them also, although I currently live in NZ, DHL is the carrier they use. ALL goods coming in through DHL are checked by customs and if the item/s including freight cost is/are over a certain amount then duty is charged, always, with no exceptions. In NZ the amount is $400. This has also been my experience when receiving goods shipped to Japan, England and Australia, although the cut off amounts vary. I would assume this would be similar in the US, seems pretty standard. Hope yours slips through ok, as others have said the freight costs are increasing and if you get stung with duty also the O/seas purchases can begin to lose their appeal, especially if you have a problem and have to return the goods. In NZ fortunately/unfortunately even with freight costs and even if we get stung for duty the price is still significantly lower in most cases than buying local, thats assuming you can even get desired gear. My experiences with Scubastore have been largely good, although they could take more care with their packaging and could be a little faster at replying to emails, still cant beat the prices and I guess they get do a ton of (and Im probably a little impatient at times) Good luck.
PS and if you order anything that will require/comes with a manual for a product manufactured in a non English speaking country I would advise you request an English manual if available otherwise don't be surprised if you receive one in Spanish.