I have ordered from several shops in Italy, never a problem. Places like Al Pascia, Bollito, Lepipe.it and a few others are set up to give back the refundable portion of the VAT (which works out to a little less than 20%), but a few aren't and if asked will usually give you a discount and a break on the shipping to put you in the same place. If you use Bollito or Al Pascia, they will charge 10 Euros shipping. Other shops might be 25 Euros. Express shipping takes three days, and I have gotten delivery from UPS, DHL and FedEx with no issues.
I have also patronised one private eBay seller who has come through with no issues twice. But there is no VAT rebate with the private sellers. Most seem to use Italian Registered Post, which takes about 10 days in my experience.
Some of the bigger eBay sellers are in fact shops, and it is always cheaper if you can find their web page and go that route, skipping eBay. As far as I know you won't get the VAT taken off if you buy on eBay.
The shops ship with full value invoices that customs can inspect. About half the time, a few days later I get a charge on my card that might read something like international services. The duty on pipes is extremely low. I have never paid as much as $6 I have never had a customs charge for a postal package, but that is a possibility
However, there is a drawback. You really don't want to buy a pipe from overseas if you don't intend on keeping it. Returns are a hassle, and shipping for US individuals returning a pipe is high if you want any reasonable speed and security. I have been told by Italians that their postal service is great at getting things out of the country but a clown show for inbound packages. If it is not to your liking, smoke it for a while and put it on eBay.
Italians have been selling artisanal luxury goods to foreigners for centuries. They are very good at it. The internet, express delivery and electronic funds transfer have made all of this a lot easier than it was when I first started doing it in the 1990's. Your mileage may vary, and I am probably due for a bad experience, but taking the long view, things average out.
And just to add, despite shopping carts and list prices that make you think you are buying in a fixed price environment, you aren't. Everything is negotiable in Italy. Everything. Contact the shop by email,ask for the net Euro price delivered to the US, then start whining. A good opening is to complain about how weak the dollar is against the Euro right now (it is). That's a good starter.