I have, a few times; before the current tariffs.
Most items were below the price cutoff IIRC.
I did buy something from Thomann that required customs / import duties (which was worth it because it cost nearly half the price of what US retailers were selling it for, with the customs charges included!).
The US shipper sent me a bill via email; I paid it, and the item was released. Same thing recently buying a guitar from Japan a few weeks ago; US shipper sent me the customs bill, and I paid it which released the shipment.
Canada is another story. I purchased a guitar from a Canadian retailer, and we couldn't get it through customs; it was returned to the seller twice (a music retailer, not a private seller), and I asked for a refund.