Do I need a return flight booked to apply for a multi-entry tourist visa for Thailand?

I don't think Brandon's input is correct. Why would you have to show a ticket out of Thailand within sixty days, when you can get a thirty day extension onto your initial sixty day stay. Also, why would you have to show another ticket back into Thailand after your initial visit? I got a non-O immigrant multiple entry visa and flew into Thailand on a one-way ticket. Multiple entry visas doesn't mean you have to go into any country multiple times. It's up to the visa holder whether they want to make more than one visit.

To apply for a multiple entry tourist visa you must provide proof of why you need multiple entries. This means showing a ticket to Thailand, a ticket out of Thailand within 60 days, and another ticket into Thailand. If you do not supply this then you have not shown that you need multiple entries, and they may issue you a single entry tourist visa and keep the higher amount of money that you paid.