Voidable marriages in Thailand are not very common. These marriages may have occurred if one of the parties had been threatened to marry another. Forced marriages or marriages under duress are voidable marriages. Any marriage that had been done under duress needs an annulment and not a divorce.
Property rights with regards to voidable marriages and annulment are covered elsewhere on this website. There are a number of incidences where an annulment would be an option. This occurs when the marriage does not qualify as a valid marriage under Thai law. These would be as follows:
1. You got married to a woman you did not know was insane. Insanity is declared by the courts and you would need to show that she was already declared insane before you had married her not knowing this fact;
2. The person you married in Thailand is your sister or close relative and you did not know this;
3. You got married to a woman who was already married. The district office would pick this up however she got legally married in Malaysia or Cambodia to another and then married you as well then this would require an annulment. You would need the documents to show when and where she legally got married before you;
4. You married someone who was forced to marry you;
5. You met someone on the internet and met them in Thailand. You got married to her and you only later discovered that the person you spoke to for years on the internet is not the woman you got married to.
6. Mistaken identity does happen when you met someone and got married to her only to discovered that you married her twin sister;
7. You got married to someone who was under the age of 17 and did not know this at the time. This would not be common as the government would check during marriage registration in Thailand.
There are a number of incidence where annulment becomes an option. They are very rare in Thailand however they do exist and the laws are in place for when these should occur. Voidable marriage are rare and annulment is rare as the district office that register the marriages would detect the first signs of problems. Mistaken identity in the internet age is becoming more common however these tend to be more online scams and do not end in marriage. If you are considering an annulment then speak to a divorce lawyer or family lawyer in Bangkok for more assistance and guidance.