That's not what happens. You see the price tag, you just don't buy it, is what happens.
That's not how tariffs work.
You pay the sticker price, which does not include tariffs. The package ships. It arrives at the US border, and the carrier (DHL or whoever) bills you for the import tax before it leaves the port.
Maybe this will change, but up until now when importing things, tariffs were not part of the price paid to the seller.
I see some ways this could be exploited.
Let's say I have a nemesis, I could in theory spend 100$ in packages from China, and ship it to them. And they'll have to pay 245$ in tariffs ? (245% today).
It's not exploitable in that way.
The bill received is a "you must pay this if you want the package. If you do not, we will destroy the package". It's not a contractual obligation where you get sent to collections or take a credit hit if you don't pay.
In the situation you described, the end result is that your nemesis does nothing, pays nothing, and you are out $100.