Between countries, a wire transfer. It’s not expensive.
I recently did a few wire transfers out of country related to distributing my late father's estate.
Each transfer cost about $45 (CND) in bank fees regardless of the total amount being transferred.
This might be worth it for a more expensive item, but in northernguitarguy's case, he's selling a small amp for around $350.
If you add on wire transfer and shipping fees to a US destination, it would probably be easier and more cost effective for the customer to just buy one locally.