Found a cheap flight online that's almost too good to be true? It probably is.

"Drip pricing" is used to suck in consumers by advertising cheap headline rates, before automatically adding on fees and charges such as credit card surcharges, travel insurance, car hire, checked baggage and carbon offsets when you try to pay online. Many airlines bombard you with lengthy forms, often pre-checked to include unnecessary optional extras.

We show you which sites to be wary of and how to avoid paying for options you don't need.

Video: Travel surcharges

Jetstar

Jetstar's online booking system is inconsistent. Consumers must opt in to agree to terms and conditions, prepaid parking and SMS itineraries. But they must opt out of loyalty club membership, seat selection and checked baggage (so make sure you click the right box if you've only got carry-on luggage).

CHOICE staff member Linda Magee recently booked a family trip with Jetstar. While the fare seemed cheap at first, she was shocked to find a number of extras she hadn't realised she'd opted in for had been tacked on to the end of her bill. "I selected seats without realising they would cost extra," she says.

"It doesn't look like you have to pay something on top of the fare when you go through the steps, so I couldn't believe it when I saw it on the bill at the end. By the time I realised what had happened, I'd wasted so much time on the booking process that I didn't really have time to start again."

But this was just the beginning; Linda was then stung by a $60 credit card payment fee. "I don't have a Jetstar credit card, but I didn't realise that it would cost me that much more to pay with my regular card. I paid up, but I won't be flying with them again."

A spokesperson told CHOICE: "Jetstar clearly discloses any charges and provides customers the choice to customise or remove any offering. We disclose this fee and fee-free payment options so there are no surprises."

Qantas

Qantas' online booking system is the most transparent and easiest to navigate.

Consumers have to select whether they accept terms and conditions, want to purchase travel insurance or carbon offsets, receive flight specials by email or have the website remember their details for next time.

Regional Express

Rex, the airline servicing Australia's rural flyers, has a booking system that can be tricky to navigate. Consumers opt in to receive their itinerary via SMS and for additional services such as transporting unaccompanied minors.

But if you're in a rush, you may not notice you must opt out of buying travel insurance. As with all policies, customers can cancel their purchase within 14 days, but this is a trap to watch out for.

Tiger Airways

If you're not careful with Tiger's online booking system, you may be paying for extras you neither want nor need.

Users opt in for terms and conditions and the carriage of sports equipment, but opt out of checked baggage.

"The booking options available on Tiger's website are based on customer demand," says spokesperson Vanessa Regan.

Interestingly, sometimes during our testing we had to opt out of travel insurance, while other times buying travel insurance required going to a separate site.

A pop-up window advertising the option to switch to flexible ticketing, which allows flight changes but is very pricey, also interrupts the booking flow.

Regan says consumers need to be aware of the options they're selecting in the booking process. "We encourage people to select carefully to ensure they tailor their travel needs correctly at the time of booking."

Virgin Australia

While most of Virgin Australia's booking system is straightforward, there is some trickiness. The box to opt in to Velocity Rewards, Virgin's frequent flyer program, looks an awful lot like the terms and conditions box.

Customers must select whether they agree to terms and conditions, wish to check baggage, offset their carbon footprint or pay for extras such as seat selection, yet travel insurance is automatically selected, so you have to specifically opt out if you don't want it.

Virgin spokesperson Melissa Thomson says customers who buy travel insurance without meaning to can cancel their policies. Virgin even sends customers an email informing them of their purchase and allowing them to reverse it after an online booking is completed.

"We're fully supportive of travel insurance and thoroughly recommend it to all of our guests. But if they wish to, they have 14 days to cancel the travel insurance."

Would you like insurance with that?

Many booking sites automatically assume you need travel insurance. Regardless of their questionable tactics of opting you in, it's highly recommended that you take out insurance - whether through the airline or your own choice of provider.

It's worth checking your options before you commit – after all, the one-size-fits-all policies that some airlines offer may not cover you for pre-existing issues, if you're over a certain age or in other circumstances. Always read the product disclosure statement before buying any travel insurance.

Tip: You may already have travel insurance provided when you pay with your credit card. Check with your bank.

ACCC crackdown

The Australian Competition and Consumer Commission (ACCC) is cracking down on drip pricing across a range of travel industries, including airlines and hotels. After launching an investigation in November 2013 in response to complaints, the consumer watchdog said in February 2014 that it is likely to take legal action against some companies.

Under Australian Consumer Law, you are entitled to see the total price of a booking, inclusive of any additional fees, charges or taxes.