the embassey wants a 'certified translation for the thai docs.. do you just goto any legal office for that?

Which country?
 
For some, like the UK, a certificate by the translator is sufficient.
 
From the UK's Guide to supporting documents

If you submit a document that is not in English or Welsh, it must be accompanied by a full translation that can be independently verified by the Home Office. Each translated document must contain:
 confirmation from the translator that it is an accurate translation of the original document;
 the date of the translation;
 the translator's full name and signature; and
 the translator's contact details.

 

Others, like the Schengen sates, require certification by the Thai Ministry of Foreign Affairs.

tx..its for USA..

Sorry, I don't know what the USA require.

"the embassey wants a 'certified translation for the thai docs.. do you just goto any legal office for that?"

 

I would say NO. Just as the MFA requires that all translations sent to them must be done by a registered and authorized legal firm for the MFA. If your in Chiang Mai 100 meters east of the US Consulate on the same side of the street is Star Visa. They are registered with the MFA and do english/ and Thai/English translation for both the MFA and US Consulate.

http://www.starvisa.net/en/contact.html