Everything depends on your previous travelling history. This is the way a six months multiple entries tourist visa for pure tourism is suppose to work. If you have a history of short stay entries or travel back to back on METV’s you could easily be taken aside and questioned. A IO could also suggest or insist that you stay more time outside Thailand before you do a new re-entry. Personally I would maybe have considered to use a landborder transport company for the last border bounce to be safe.
It’s not just about the correct documentation. Krungthai demanded as an example that I did the first year extension of stay on my 90 days Non O for opening a bank account. That’s not easy without a bank account unless you get a affidavit letter from your embassy. An agent can still open for you while your on the initial visa.
Never done it myself, just seen it (couldn’t find it now), but they confirm both your personal information and your income reported to the Norwegian authorities in gross income before taxation.
This is what you have to provide to get a affidavit letter from the embassy and you see it’s called a "check list for income confirmation". (NAV is the general pension provider in Norway). They verify and specify your income as it’s reported to the Norwegian authorities. Never heard of any affidavit letters turned down by the immigration, and as I understand it’s considered as a guarantee of income as some immigration officers have referred to it (according to a Norwegian/thai newspaper) and its the only document they accept even though they do also a control of the original documents.
At least at the Norwegian embassy in Bangkok you’ll have to provide your complete tax settlement from last year or annual statement from your pension provider and proving your income to get a affidavit letter. I’ve never heard of any problems regarding this as it’s used by people staying in Thailand for decades, but as mentioned some immigrations might require a legalization for your first affidavit and you also have to show the original document provided to your embassy.
Some immigrations require a legalization from the Ministry of Foreign Affairs for your first affidavit letter. You normally also have to show the original documentation you provided to your embassy.