You can find loads of PTC blogs etc., which are recommending well paying PTC sites for you. You should understand that these recommend lists aren't necessarily up-to-date, what was hot PTC site six months ago, could be currently on it's way to be virtual ghost PTC.
How to recognize potential scam?
Here are some things for check-list:
- just few ads to click and most of them are just linking to other PTC affiliates
- pay per click for free member is more than 0.01
- design looks cheap or it is direct bulk "bux" copy
- is website running on free host or own domain?
- if TOS is suspicious or it doesn't even exist
- suspicious earning logic, do your math
- use http://www.whois.net/ for googling domain owner
- bought referrals are bots
Check some of other websites for more tips:
getpaid-ptr.info and
ptctalk.com, pctalk.com forum's guide -
how to spot the bad new site and so on...