Finding whether two eCommerce customers are same physical entity? <p>eCommerce sites sometimes give some deal which can be used only x number of times by a particular customer. Without any exception there are some clients who try to create multiple accounts to use the same deal more than once, and sometimes gets caught. I would like to how the eCommerce site maps these accounts/digital addresses to a single physical entity. </p> <p>I Hope this is ubiquitous to all eCommerce site and has been explored in deep . Can anyone point me to some reading material on this? I googled but did not get anything (yes , i don't know what should be my search query)</p> <p>Thanks in advance </p>