for example, check this out 

https://www.ebay.com.au/itm/264543756601?hash=item3d98096139:g:gzIAAOSw-GtdFxeR&amdata=enc%3AAQAIAAA...

its $7.99 for one tshirt with free postage, where as only postage charges for this t **bleep**s is more then $9.
Hows it possible?
there are many items for less then $5 with free shipping.