How are the members cheating the PTC sites?

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If we enter into the forum of the ptc sites, we are able to see many topics started by the admins about the cheaters in the site.I am just curious to know about this.How the members are cheating the ptc sites? By doing so what are they getting? Because multiple accounts can be found and removed at any time and they can not request any payment from the site.Even then the site owners are mainly concentrating about the cheaters. Are there any real cheating members or else , are the admins are saying so to avoid the payments?As we have some of the ptc admins who are active in mylot, I hope we can get some information about this.