Det verkar som om den informella politiken förändras.
Som Wikitravel nämns :
Proof of onward transit :- long happily ignored by Thai immigration, has been known to be strictly applied in some instances (Indian passport holders beware). The requirement is for an international flight itinerary - NOT train, ferry, or other departure type. Airlines, who have to pay for your return flight if Thai immigration doesn't let you into the country, also check this and often will not let you board your flight for Thailand without it.) A print-out of an international e-ticket on a budget airline is sufficient to convince the enforcers, but those planning on continuing by land may have to get a little creative. Buying a fully refundable ticket and getting it refunded once in Thailand is also an option. Land crossings, on the other hand, are a very straightforward process and proof of onward journey is generally not required (Indian passport holders beware again... or anyone, if the border officials simply decide to uphold the bureaucracy).
Eftersom din biljett är ute efter 30 dagarna av viseringen, kommer det att höjas en flagga - de kommer att undra om du planerar att överstiga. Du kan visa bevis på boende bokat på andra ställen om du har det eller annan transport bokad, men det finns ingen garanti.
Så lång historia kort du kan vara ok, men din bästa insats om du vill vara säker, är att använda skyscanner eller kajak, hitta det billigaste eller återbetalningsbara flyget från Thailand till var som helst , boka det och använd det som ditt "bevis" att du lämnar. Sedan avyttra det eller få det tillbaka.
Från Thailändska ambassaden :
You "must have a confirmed return ticket to show that they are flying out of Thailand within 30 or 15 days of entry, as appropriate. Open tickets do not qualify. Travelling overland out of Thailand by train, bus, etc to Cambodia, Laos, Malaysia (including en route to Singapore), Myanmar, etc is not accepted as proof of exiting Thailand. You may be asked to show your flight ticket on entering Thailand. If you do not possess a flight ticket to show you will be exiting Thailand within 30 or 15 days of entry you will be most likely to be refused entry."