First of all, immigration never asks about return or onward tickets only the airlines. It is an official rule which is why airlines ask as they have to fly you back home if denied entry. It's not a policy decision of the airline but just depends on how sharp your check-in agent is. The rules for travelling are supplied by IATA and appear on the screen as you check-in. I recently travelled to Perth WA and on the return flight to Bangkok my wife and son were denied boarding as they didn't have a return/onward flight (I had a re-entry permit). They had travelled on their UK passports but both are Thai citizens so on producing their Thai passports the problem went away, but my point is they WERE asked so all the ppl who say I haven't been asked in 20 years are not helping anybody. BTW you are overthinking it so don't offer up your $12 ticket unless the check-in agent asks and at immigration just hand in your passport and boarding card for the flight you arrived on then he/she will stamp you in for 30 days. Enjoy.