In addition, most PTC sites offer a commission to its members for signing up new members (similar to many affiliate marketing programs online), or they may pay members a percentage of the clicks that their referrals make as an ongoing commission.

The viability of the PTC business model has been questioned, as fraudulent clicks have ramped up the expenses for advertisers.^[1] With lawsuits filed against the internet search companies, the burden has been placed on Google, Yahoo and others to determine valid clicks from fraudulent ones.^[2]

This should not be confused with PPC where advertiser pays the site per click generated from any user.

Even though advertisements are the most widely known method for PTC sites to stay alive, much of the profit can come from the direct sales of referrals or upgrade packages which are created by the owner of each PTC site. This has led to the proliferation of online scams or ponzi schemes being created with PTC sites as a cover, as members are encouraged to buy referrals that are not actually human or upgrade packages that offer no real value.^{[citation needed]} As well, some sites^[who?] may request that their users pay an "upgrade fee" before being able to cash out their earnings, and then not paying out earnings after these fees are paid.

Scams, although exposed on various PTC forums, are still heavily used by newcomers who are drawn in to the websites by search engines. Scam PTC sites are known to attract new users with cheap offers for upgrades and referrals and disappear without trace after a short time.^{[citation needed]}