I agree that the seller should combine shipping costs if she can.
But I also agree that it is up to the buyer to confirm the cost of combined shipping.
To be very very pedantic, putting several purchases in one box is a form of 'combining shipping' even if the fees are unchanged.
It is also important to understand that combining shipping may make the postage higher.
I can ship a 2cm thick/ 300 gram paperback to Ontario for $2.95.
Two books would cost $20.24 cents to ship together. (I would have tracking on the heavier parcel.)
https://www.canadapost.ca/cpotools/apps/far/business/findARate?execution=e1s2
Ask-- don't assume.
