Easy ways to know ponzi scheme is look their interest rates. If any financial investment offer 100%, 200% or higher ROI within a month, it's just a ponzi investment. So, stay away to invest from this kind investment service.
The higher the profit, the more likely it is to be a scam. Earning money was never easy so I doubt people don't understand that. Even the 100% ROI could make some people think twice before investing already, let alone the higher ones.
Ponzi schemes are easy to spot nowadays due to the sheer amount of related projects before that have gone down the hill and the never-ending low stakes, high reward business model which they use to lure in people, especially the newbies. Even though they are easy to spot, they still pop out every now and then around this forum and the newbs keep on investing due to the offers. In order to avoid such, my advice is to ask how would they make money and pay their investors, and if they answered the generic “we will invest this on X to gain Y amount” then you know they are not someone to be trusted with.
Well, newbies are the easiest people to scam after all. Not only newbies but rather ignorant ones that don't understand how legit projects actually work and progress from the start-up to them starting to profit. Rather than letting themselves succumb because of their lack of knowledge, I'd rather advise them to buckle up and study a lot, learn how to differentiate a scam from a legit one.