Can i make as much $ without investing $ on the ptc sites?

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As mentioned above. As i have noticed that most of the people who make alot from the ptc sites are actually investing money into the ptc sites and therefore that's how they manage to earn so much? Can i without investing money into them earn as much too? As i'm afraid that investing $ into these ptc sites might end up losing $ as you never know when they will close down.