They will lie to you that they cannot withdraw bitcoins from where they are and need to get someone to assist them, then they will send you a link to a site of which they will transfer the amount into your account on the website. Upon withdrawal of the bitcoins the account will opt you to have a blockchain account and add an extension known as cashback. when you load you blockchain wallet they will withdraw the amount instantly as the extension gives them access to your blockchain account and everything inside it