I heard that DeepOnion is a scam. Is it true?
It's a scam such as it does not have any anonymous features it is advertised for. And there are 18 millions of premined coins in the hands of a few anonymous "developers". That's the only anonymity in this coin.
Nevertheless you can make easy money with it. Either by just buying and let it sit for some time, or by arbitrage trading. The latter becomes more difficult as the volume now goes up. Premined coins are getting dumped now into the market. So be careful what you do and get out in time.