[azstar]

Many countries require a return or onward ticket before they will allow you to enter. It is not within the airlines control if this is what the country requires. You could be deported (at airline expense) and the airline will be subject to a huge fine (frequently up to $10,000 for each passenger who arrives without proper documentation.)

You could purchase a fully refundable ticket (it will be expensive) and get a full refund when you return to the USA, or buy a refundable ticket to a country near Guatemala (Mexico, for example). That way you can enter the country, and purchase any kind of ticket you want once you get to Guatemala.