Another option, is that if you have reached enough Clicks ( that is, earning funds from clicking ads, winning from the ClixGrid, accomplishing Tasks and/or Offers ) these get accumulated in your account -- you can use this to get your Premium
To see if you can get the Premium, hover your mouse/trackpad pointer over your account name at the top of the page ( just next to theSign Outbutton ); from the drop-down menu, click on the Premium Account -- this will lead your to the Premium Account page, where on the upper-right corner is where you'll see a link where you can get the Premium ( if you reach the requirement of $17, the link button will appear )
Have you checked with Google AdSense Program Policies and TOS ( Terms of Service )? Perhaps under their rules and guidelines that there might be something why they prevent/block such
There are sites that research on the status of a PTC site ( especially once they know a new one has entered or being created ) -- they do a rundown of how the said site offers it's services, it's modes ( and frequencies ) of payments, it's forums, interactions and so on -- so a quick browse over the search engines of your choice can give results of both good and bad views about the site in question
Since there's so much data, you'll have scrutinize the words; for example -- a lot of forum and blog posts are made talking about a paying site, and these posts carry both good and bad views about it -- it'll take time to make a decision, but along with gut-feelings and knowing it helped me
Let me share an experience I couldn't locate my own thread about it at this time ( but it's somewhere in the General Talk area ) that there was one case I heard from a friend who signed up to one; she was a Premium user for that particular site had problems with her ads and payment, and went to create a Ticket for the site -- but upon submitting, the site requires her to pay $1 for a Ticket completion ( Really, assistance from the site's personnel wasn't there -- just an automated message ) and to add to that, there was no Forum she could ask help from the members -- just a Facebook page to link where one could 'Fave' and keep up with the updates
Thank goodness the site was already closed down ( featured on local news, it was an eye opener for her indeed -- not only she told me that she had to fork out a Premium payment in cash to a local branch via walk-in to join the site to earn, but her 'so-called' earnings for a few months were all for nothing -- a waste of time and resources )
So, that my two-cents "If it sounds too good, it is"