For most sellers here, they are sending smaller and lower value items that often go through customs & are delivered without being billed for customs fees/taxes when shipped via the postal service.
If a package is shipped through USPS and gets stopped in customs (it's pretty hit or miss for most countries, though England, Germany and Italy are pretty consistent for packages being stopped for charges). There is a handling fee of usually around $5 USD, plus whatever taxes are owed (like sales tax in the US).
If you ship through a courier, it always goes through customs so the customer will always owe the brokerage handling fee and customs fees.
FedEx and UPS (United Parcel Service) are private courier companies that charge international customers brokerage fees for presenting the package to customs in the destination country on every package.
When you pay for their fast services, the customs brokerage is usually worked in to the shipping price you pay--part of why the price is so high.
When packages are shipped using their less expensive service--like UPS Standard service which would be the most likely way these smaller/low value items would be sent, the package still goes to customs but the recipient receives a notice to pay the brokerage directly.
The couriers don't tell the person sending the package about the brokerage fees, usually both the sender and receiver find out about the fee when the receiver gets a notice in the mail to pay brokerage fees in order to get their package. If the receiver rejects the package because of the brokerage fee, the courier will try to collect the fee from the sender.
Here's an example of the fees UPS charges Canadian recipients:
http://www.ups.com/content/ca/en/shipping/cost/zones/customs_clearance.html