From experience.
If you are shipping across a border you need to think about shipping cost, customs duty AND there is an import/customs handling fee (where you have to pay for the service of paying the customs duty).
All these costs should be considered when pricing up.
You can get hit with customs duty, even if the item is duty paid in the original market.
And so you should ask the seller about not paying purchase taxes or VAT.
If you are going to hop across the US border, include the gas money in your calculations. Unless you can combine it with another purpose, like a trip to see uncle Buck.