@YOSHIE have already given you the format of reporting a cheater or an alt account. But I would suggest you should venture your precious time into doing something very meaningful because finding accounts that have shared gas to each others isn't bad though but is very risky. However sending gas to another address doesn't fully shows that such person is a cheat or using alt, for such claims to be valid is when a user using same address or same telegram id and with same facebook profile in enrolling same campaign that could be automatically proven is true. I had a friend who told me in their office they do teach people how participate in bounty and as well also sells their rewards and then give them their payment in our local currency. Why because most of their students are not yet familiar with the exchange process of moving and converting their tokens. At such point what would you do?

So be very mindful while sourcing out address that sent gas to each others.