A friend of mine fell for the Brussels Airlines "Lowest fare guaranteed".
Despite complying with their terms and conditions to the letter (the t&c were studied thoroughly), they nevertheless refused to give him back his money.
According to their guarantee, they will supposedly beat a competitor's price by %10 if you purchase their higher fare instead of purchasing the same (but cheaper) ticket at a competitors' website.
Sounds simple? Well as all things in life, what sounds too good to be true, generally is exactly that: Too good to be true.
Don't fall for it!
The customer service representatives are all nice, courteous, helpful and promising up until the moment you book the flight and they have your money. Once you punched your credit card into their system, you can probably forget about seeing a single penny back from them, despite all of their promises.
I wrote a blog post with all the details. Hope others can learn from this and avoid falling into the same situation.
http://bgreenson.blogspot.com/