I've heard of booking.com and travel agents aka aggregators. (And I do frequently end up booking with a hotel directly.) However, I've also booked packages of various types through specialized agents that would have been very difficult to have done myself if even possible. So I don't think there's a general rule.

I do expect that there is a general rule with a lot of things that if you're fishing for deals that are too good to be true sometimes you'll be burned.