It is the dream trip, the one that took years to save up for and now nothing can stand in the way.

Once at the airport and the bags are checked, the sound of that sentence makes the heart beat in joyous jubilation.

However, before boarding, one attendant says "sorry sir, but sue to overbooking the flight, we do not have any room."

Does this sound sketchy?

Well, it is something that happened to Air Force attorney, Tom Posch.

According to frommers.com, Posch missed a weekend trip to Cleveland last summer after United Airlines overbooked his flight. 

In the cases in which this has happened before, passengers usually accept  the airline's offer of a flight vouchers as compensation, but Posch, refused United's three vouchers worth $300 each, according to frommers.com, deciding instead to go to federal regulators and find out exactly what the law requires the airline (United) do in this situation.

What he found led him to file a lawsuit in a Virginia district court last month and revealed that passenger rights are never a sure thing -- even when it comes to something as seemingly certain as involuntarily denied boarding compensation, reported frommers.com.

United says he's misreading the rule: The involuntary denied boarding rules include an exemption for aircraft with fewer than 60 seats, and since his flight was on a 50-seat regional jet, the airline didn't have to give him anything, reported frommers.com.

However, Posch believes that not only should he have been offered more, but that United the 60-seat standard applies only when extra passengers would interfere with the aircraft's safety, according to frommers.com.

Frommers.com adds that fortunately, involuntary denied boardings -- or being "bumped" from a flight -- are relatively rare. Airlines record each incident and must share it with the Transportation Department. The DOT then publicly reports the number.

Among the major carriers, United had the most involuntary denied boardings from July to September, the last months for which figures are available. It bumped 4,014 passengers, for 1.9 bumpings [sic] per 10,000 passengers. By contrast, JetBlue, with the fewest denied boardings, showed just 10 passengers the door, states frommers.com.

The DOT did discuss and strongly consider banning overbooking flight in 2011, but later came to the decision to just raise the penalties.

To not fall into the Posch trap, read the fine print before booking the flight.