I'm traveling to los in november on my koean air miles.I only have enough points for a one way ticket,I plan to buy my return ticket there. How risky is this now.I've been to los many times but I can't remember if they ask to see your ticket t immigration

very rarery - just tell them you have an electronic reservation (e-reservation)

You are much more likely to be quizzed at check in before you leave. In Countries like Australia, USA and UK they will not let you board unless you have a visa (residency) or an onward ticket. Doesn't happen so much when traveling to BKK from an airport in Asia. The easiest thing to do is to get a travel agent to make a booking for you out of BKK, you will get an itinerary (for an electronic ticket) and then cancel it (dont pay for the booking). This will be enough to get you on the plane.

Good luck.

As already mentioned, just get a tourist visa or have a print out of an e-ticket for the return leg.

out of tens of times they asked me only once - I hadn't got even print out (not required by the airline)