this miner web site is a scam and those people are spamming the board with this type of message.
I've tried mining contracts before and its almost impossible to get profit from them. Which begs the question, if it was profitable why wouldn't the mining site just keep the currency and profit that way?
Genesis-mining is a legitimate mining site but looking at the cost of their zCash mining contract it would take the full year to make your money back. And if zcash's price tanks, you'd really be screwed.