Gerard of this forum has had the bad, I recall, experiences on buying from England........
I have been buying from the UK since around 2000, but that's primarily due to the fact that I also own Morris Minors, and that parts for Morris are much ore limited in the US. The recent (and still unresolved issue) is not with the seller or the shipper, but with the carrier (FedEx). Technically, duty is not charged on vintage auto parts, but much of that depends on the shipper labeling them properly, and the shipper/carrier knowing this. Some carriage companies know this, but still charge duty erroneously. No one will "guarantee" you not being charged duty, but except for certain carriers, it doesn't happen.
FedEx lost my $2000 box of parts, not once, but twice in the same facility. Maybe I'm cynical, but I believe it was either a case of extreme neglect/indifference or flat out theft. I have seen photos of the box, contents and shipping receipt sent to me by FedEx for verification, and upon confirmation, was promptly lost again before leaving the facility. The fact that it was never scanned after being received in Memphis makes me all the more suspicious.
As of today, I have been asked for 4 different iterations of the shipping contents receipt, each time FedEx finding fault with some minor details such as how the receipt is labeled. For example, yesterday they requested a new set to be labeled "Replacement Cost Invoice". This request comes 6 weeks after the last set of invoices (3rd time) supplied directly from the seller in the UK.