to be accurate this has nothing to do with mining!
basically the scammer asks you to give him your private keys and then asks you to send coins to those keys, and if you do, the simply steals them. the scammer in this scenario is using combination of greed plus lack of knowledge (or laziness to do research) of the victims. otherwise that excuse they use to get your private keys is very easy to detect, it doesn't matter if they are using mining as an excuse, trading (API keys), doubling bitcoin,....