Stuff like Bang Bros etc.. Shady looking sites should be avoided – even if they have good adult-aged stuff – could be a trap – but I guess most don’t run into stuff.
Also there’s no such thing as a trap. There are no pages with teenage girl CP that claim the girls are over 18. Even if they existed, no one who visited those pages would go down as long as the girls look like they could have been 18. Think about it again. Why in God’s name would anyone put underage teenage girls on a porn site and then claim they were adults? What would be the point? How would that get you more traffic? It doesn’t even make sense.
If the site says they’re all over 18, quit worrying and look at that stuff all you want. There’s no such thing as “CP traps” on the Net. Entrapment is illegal anyway.