Hidden airline fees are the reason the cheapest fare on the screen is so often the most expensive trip. The number you see is the start of the bill, not the end of it. By the time you've added a bag, a seat next to the person you're traveling with, and a little insurance against your own plans changing, the "cheap" fare can quietly pass the one you scrolled past for being twenty dollars more.
This isn't a trick anyone is pulling on you, exactly. It's just that the price you compare against is the one piece of the trip the airline can control down to the dollar, so that's the one it advertises. Everything else gets bolted on later, after you've already decided.
Where the real price hides
Start with the bag. A basic economy fare that looks great usually assumes you're flying with a backpack and nothing else. Add one checked bag each way and you've often added thirty to seventy dollars, sometimes per leg. Then the seat. On the cheapest fares you don't get to pick one for free, and if you want to sit with your kid you're paying for the privilege. Change fees are the third one. The cheapest tickets are usually the least flexible, so if your dates move you either eat the fare or pay a chunk to shift it.
None of these are scams. They're just real money that the sticker price politely leaves out. The honest comparison is fare plus the stuff you actually need, not fare alone.
Do the add-on math before you book
The fix is boring and it works: total the trip you'll really take, not the one in the ad. If you check a bag every time, add the bag to every fare before you compare them. A slightly pricier ticket that includes a bag and a seat assignment can be the cheaper trip once everything's counted. This is the same reasoning we use when we weigh what a layover is actually worth: the posted number and the true cost are different things, and only one of them matters.
What we do, and what we don't
We're not going to pretend we can itemize every airline's fee chart for you, because they change and they vary by route. What we do is send you a few real options side by side every morning, so the cheapest sticker isn't the only thing you see. The second or third fare in the email sometimes wins precisely because it already includes the bag you were going to pay for anyway. Read the whole price, not the first line of it.