There are a lot of scam PoS coins and Masternodes.
They promise you a ROI with 30 days... you can look at www.crypto-coinz.net/ for a lot of masternode coins. But you will see what I mean
You should go for safe projects like Ethereum. Ethereum is not PoS currently but will be in the future, or NEO that produce GAS.
Yes probably ,scam PoS coins or Masternodes are everywhere now and as you said that they promise that they will return your investment,actually in my own opinion theres a 70% that they are legit project but the remaining 30% are the chance that they will scam you,and if you will go for like this token you should think twice because there a lot of token that will bring you and income and great future.They promise you a ROI with 30 days... you can look at www.crypto-coinz.net/ for a lot of masternode coins. But you will see what I mean
You should go for safe projects like Ethereum. Ethereum is not PoS currently but will be in the future, or NEO that produce GAS.