One of the more recent additional cost options to come to the fore has seen some airlines charge a premium to reserve seats on their aircraft.
In the United States, Delta, American Airlines, and low-cost carriers U.S. Airways, Frontier, Spirit and Allegiant have implemented charges for "preferred seating."
In Europe, budget carrier Ryanair began offering specific seats at an extra cost earlier this year. Its low-cost rival Easyjet has also started to experiment with the practice.
"(This is) something many airlines used to allow you to request for free," says Gray. "So incurring charges for these now is irritating, especially for families who are told they have to pay to select seats so they can sit together."
According to Heimlich, however, these charges again provide the customer with more choice in what they do and do not pay for.
He says: "In baseball stadiums, for example, you pay different prices for obstructed and unobstructed views." This is now the same with airlines, he adds.
Credit and debit card surcharges
A common complaint of those booking plane tickets online is the unavoidable charges that often accompany paying for flights by debit or credit card.
The UK government's trading and competition authority, the Office of Fair Trading, last week ruled that debit card surcharges must be included in the headline price of flights.
Budget carriers including Ryanair and Whizz Air have since agreed to amend their online booking policies to reflect this. But elsewhere the practice remains.
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Flexing the plastic on Australia's Jetstar adds an extra $8.60 to flight prices, while a similar transaction with Air Asia costs $6 in card-usage fees.
Prominent industry players such as British Airways ($7) and Air France ($7) meanwhile charge for those using credit cards to make online reservations.
"Surcharges for credit or debit card payments are ... especially unfair," says Gray. "We accept that retailers incur some costs when faced with things like processing card payments, but the charges passed on to the consumer are often excessive."
The idea that customers aren't aware of these charges doesn't wash with Heimlich however.
He says, "I'm not sure where the confusion arises at this point ... fees are fully disclosed on websites. In any case, the airline industry only endorses transparency (in these matters)."