Two situation which come up....
1 - you are asked to use the recipients DHL/UPS/FedEX account number.
This is a bad move, the account number is usually "borrowed"
2 - you are provided a prepaid shipping label
This is usually ok, the recipient is the on the hook
If you have concerns check with the shipping company when you get the label, they can tell you if it's legit.
Companies like DHL/UPS offer HUGE discounts to their big customers, if your buyer has access to these discounts the shipping costs may not be anywhere near as high as the retail counter rates.

"What else could I do? I had no trade so I became a peddler" - Lazarus Greenberg 1915
- answering Trolls is voluntary, my policy is not to participate.