I'm not sure how "goods to follow" would work in these situations where it's actually "people to follow". At least with the goods following, you show up at the airport and declare $300 of stuff with you, and another $450 is on order and will be shipped at a later date.

But if you ship $750 of stuff ahead and claim that as your allowance, what stops someone from also showing up at customs and declaring the $750 of stuff they have on them as their allowance?

"goods to follow" mean exactly that. You are declaring good that are to follow after your declaration.
One cannot ship stuff ahead of time and use the goods to follow declaration method.

There are custom brokers who specialize in these regulations and can advise as to the best method/timing and the proceeding and classification to make the declaration under to minimize your duty exposure.

I get that. I was just confused because the advice about "goods to follow" in this thread doesn't seem to fit the situation where the OP is talking about sending his stuff back before he comes back. If you are able to ship stuff back under your exemption, what's to stop that person from also bringing stuff back and claiming that under their exemption? Surely that system can't just rely on the honour system?

The goods shipped prior to return would theoretically have duties and taxes applied them upon clearance into Canada. No expemtions would be possible for the release of the goods (barring that they were not obvious gifts, in which case the $60 gift exemption may apply). Upon their return to Canada the traveler would indicate on his/her declaration card that they have shipped goods or have goods to follow. The Border Services Officer would then complete and provide the traveler with a form indicating that they are eligible to benefit from the transfer of a personal exemption for goods that are not accompanying them. The amount of this transfer could be up to $750 minus the value of any goods accompanying them upon their return. The document clearly specifies these two amounts as it shall be used by another BSO or the CBSA refund department once the traveler clears the goods or applies for a refund on duties and taxes already paid.

Wondering if someone can explain the process is at customs when you tick "I have shipped goods that are not accompanying me" as yes.

We're trying to travel fairly light during our upcoming trip and was thinking about shipping back anything heavy/bulky that we purchase abroad since space might be at a premium. However, I don't want to get stuck at customs for an hour filling out a form after being transit for over 20hrs on our return journey. Would rather just haul it back with us if that's the case.

On a similar note, to what amount can you make a purchase on say a foreign store like Amazon.com and have it sent to Canada without any taxes/duties/etc. being imposed on it?

See the post directly above your post.

Hehe. I don't believe I missed that.
Follow up questions tho:
Does the initial screening customs agent provide you with the form or do you have to go to a secondary area?
Any idea what happens if you declare this going thru the Nexus iris scan side on the way back?

The goods to follow form is dealt with at custom secondary. Nexus would only expedite the process until secondary.

Depends where. At YUL we do it at primary. It's actually the only document we complete upstairs. Saves folks a lineup in secondary, but takes a lot longer than a normal primary.

Not sure what happens elsewhere.