If you are taking the items into the USA for sale (or for delivery to a customer who has already paid for them) you still have to pay import fees.
Americans can import up to $200US (about $260+ CDN) without duty.
And since you are not registered to collect and remit US taxes, your customer is not required to pay them.
When you carry the items across the border, remember you have costs even beyond the border fees.
There is your time. The minimum wage in Ontario is 18 cents a minute. How long will it take you to drive across the border and back home?
There is also gas and vehicle maintenance.
BTW, if you don't declare those purchases, the US border guards can seize not only the goods but your car. Watch a few episodes of Border Security, especially those at the Vancouver area crossing.
Import fees are the business of the importer, your customer.
Ship with Confirmation of Delivery and pack so the box stays intact.
It's his problem.
Oh you might want to add to your listings this boilerplate that eBay gave us some years ago.
Import duties, taxes and charges are not included in the item price or shipping charges. These charges are the buyer's responsibility. Please check with your country's customs office to determine what these additional costs will be prior to bidding/buying.
