I am writing about the sites where you have to make a deposit before buy and the site offers to act as a MM in deals.
How could I know when they are trying to scam me? In general, how do I know if a MM site is trusted?
Well its too obvious to those sites that are trying to scam you, if the offer is too good to be true, that you can earn with a huge amount in just a few couple of time. And before risking any money from your wallet try to search in google ('the site's name' review) and read all the reviews there with different people so you can know if this sites are legit.