Do it yourself, the agents can’t do much help anyway, since you have to apply outside Thailand only, and you have to physical be in the country, where you apply.
You also have to supply all the documents yourself anyway, so why pay somebody else to send them in to the Embassy.
You can start making an application at
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You can pause it at any step, and start up again from where you left ( Make screendumps of every page, for extra safety).
Do not support corruption, by using agents.