......Siem Reap is a shithole. It gets hotter than any other place on earth. Electricity is expensive. Food is expensive. Fuel is expensive. The dust pollution is horrendous. The mosquito's will drive you nuts. And the closest beach is not much closer than the moon. It truly is the worst place on the planet to live.
I usually fly from Darwin to Bali and then Bali to Bangkok ( Different airlines ) Very occasionally I will be asked by airline staff at check in Darwin for proof of onward travel from Bali. It is completely random but it can happen. It is easy enough to doctor up a PDF itinerary showing onward travel.
There is a rule that you need to stay at least one night in Cambodia. You may be able to bribe the immi official to stamp you back out the same day. Then you risk Thai immi not letting you back in. And they are infinetly harder to bribe. Best to go to Cham Yeam and have a night in Koh Kong.
I never pay a deposit. I pay one year in advance and bargain hard. Landlords cannot resist that big wad of baht in advance. And you won't see them for a year.
......When the time comes I can arrange a taxi to Cham Yeam border crossing and get your luggage wheeled across for you. I can also arrange a taxi from the Thai side to wherever you want to go.