Dont forget the fact that you can exchange bitcoins for fiat,and then the way to buying clothes is really close.
If you want to pay directly with bitcoins,I think you should check out openbazzar.
There are also two services that offers to purchase directly with bitcoin from amazon or from ebay.
For the first one it is possible through purse.io, and for the second one is through the shopawl which has 4% fee.
Exchanging bitcoin to fiat still is not efficient because the third party services will take fees which isn't in favuor of buyer.
The services that you are talking about do the same thing as converting bitcoin to fiat and using it.
You pay for someone bitcoins,and he buys you the desired product for fiat,which means at some way you convert bitcoins to fiat and buy things on ebay and amazon with it.