Im not here on a marriage visa, so I have never been through that process, but my understanding is that you have to prove you are living together.
When my wife went to extend her visa in the UK, we were questioned separately by immigration officials about our married life together and told we may be visited at home by officials. We were questioned on our favourite foods, tv shows, how we spent our time together etc. Intrusive? Maybe, but they need to verify the authenticity of the claim.
Its the same in Thailand.