[55555]

This is very easy and actually quite common between Amazon and Ebay. You would list the title as Merchant Fulfilled on Amazon and when someone orders it you would place the order yourself on Half.com using their shipping address and pocketing the difference.

[zeeshanm]

To add to this, you can use Amazon Listing API to add/remove items that are available on Half.com.

[misiti3780]

how did you go about finding the items that were on Half but not on amazon though ? - manually ?

[zeeshanm]

Doing it manually is one way but not scalable. You can aggregate data either using available APIs or by scraping websites. You can list books on Amazon that are available on Half.com and give you a decent profit margin. It doesn't matter if books are already listed on Amazon. Just make sure your offer price is a little bit cheaper than the cheapest available copy.