I don't know about that specific agent, but,

1. If TA seems not reliable enough, go talk to them. Do not pay until they show you the ticket.
2. Try to find reasonable published fare. FYI, BKK-KUL-ICN-KUL-SEL on MH costs ~THB24000 (tax included), no two-person-minimum restrictions, and you can buy it directly from http://www.malaysiaairlines.com/main_TH.aspx