Since the US buyer was able to see your listing, you did not Block international sales.
But US is a special case.
It might have been better for eBay to say Overseas.
The basic problems are with shipping and with returns/Disputes.
Shipping internationally with tracking is very expensive and in most Disputes the seller is required to cover the cost of tracked return shipping.
https://www.canadapost.ca/cpotools/apps/far/business/findARate?execution=e1s1
I got an offer for my shoes that I listed on eBay. It says the buyer wants the item shipped to the US
An offer is just an offer. It is not a sale.
Measure your packaged shoes (use METRIC measurements!) and tell your customer how much shipping will be.
There is a good chance your customer will disappear.
Now.
If she asks for a cheaper service, this is very very likely to be a scam. Many cheaper services do not track, and if the customer opens an Not Received Dispute, you will lose if you cannot prove delivery (not shipping, Delivery).
The service you want is Tracked Packet USA.
With the current pandemic, all shipping is delayed. Don't over -promise and do use tracking.
When you print your label through Shippo (eBay's default), Paypal (my own preference) or SnapShip (Canada Post), you will get a small discount. This covers some of your packaging costs. The buyer sees the PO counter cost for shipping, not what we actually pay in postage.
Have you signed up for a Solutions for Small Business number yet? You will need it.
https://www.canadapost.ca/cpc/en/business/small-business.page?
