Most PTC turn out to be scams or are designed to be scams to begin with. Some are not as obvious and have fairly legit motives but don't properly think out and plan.
You need to make sure you charge enough to cover costs here is a quick example.
Keep in mind this is a very simple example and doesn't take into consideration the countdown timer of each website hit which would effect the price. The longer the site shows the more the cost.
You charge $2/1000 views and you pay out $1/1000 so you get paid $0.002/view and pay out $0.001 this is half and half
You want refferals so you rent them and you pay hlaf of the 50% you have left so 50% paid to members 25% for refferals and 25% for yourself. This mans refferals will make 50% of your users which is a lot.
You have plenty buffer room and still keep 25% + the amount people pay for rentals. This is if the refferals click 100% of the time which they won't.
This also means the users make their 50% plus the 25% / refferal so there is potential profit. This is stble and the more refferals people bring in the more you will make.
The problems comes in when places charge far too little in order to attract advertisers and then they pay out the users too much to attract them. In the end they don't plan to pay users and the advertisers get bad quailty viewers.
Hope this helps.