Normally, it is possible that you carry it through customs.
If you have paid taxes in the US, and you can prove it (invoice, not a bill), they can't charge you any new taxes when you arrive.
On the other hand, it is possible that you don't pay taxes in the US, and then you have to pay them in Europe, if you go through customs like that, you can have a real cheap Jem. But have the US sales person have it's accountant or tax consultant inform him what there should be on the invoice. He doesn't have to pay taxes to the State, but you have to pay them where you enter the E.U.
If you buy a guitar secondhand in the US, let the seller write a letter that it was a gift and secondhand. Like that it isn't possible to pay extra taxes.
For more info, contact me and my own tax consultant agency
Yes, I'm a tax consultant....