Cheap international flights?....?

I am flying to Amsterdam in October and I have done an extensive search for cheap tickets online, but I am worried about scams and hles. I found some sites like 1800flyeurope, whentofly, and airfare.com, and when I looked online for reviews it was really hard to find any. I know everyone says use priceline or expedia, etc., but these are not as cheap as the ones I have found. Could you please just tell me if you have used any of those I listed and if they are legit? Thanks!!!