Just wanted to touch on the differences between a few things.
First off there is NO such thing as a "30 day tourist visa", neither is there a "30 day visa on arrival" :O The simple way to look at it is if you didn't BUY a tourist visa from a thai consulate before you winged your way here you do NOT have a tourist visa and if you didn't pay for a visa when you arrived here you don't have a visa on arrival.
If you showed up here without having bought a visa from a thai consulate beforehand and were stamped in for free (usually for 30 days but that's country dependent) you came in on whats known as a visa exempt entry.
Visa exempt entries are available to people from 57 countries. It breaks down like this; 5 countries get 90 day visa exempt entries, 6 countries get 30 day "visa waivers", 44 countries get 30 day visa exempt entries & 2 countries get 14 day visa exempt entries.
People who enter on 30 day visa exempt entries can apply for a 30 day extension at the immigration office for 1900baht.
People who enter on 90 day visa exempt entries (5 countries), people who come in on 30 day visa waiver (6 countries) * people who come in on 14 day visa exempt entries cannot get a 30 day extension.
Visas on arrival are available to people from 21 countries.
They BUY a 15 day visa on arrival for 2000baht when they get here.
So to recap one last time; IF you didn't buy a visa from a consulate before you came and didn't buy a visa from the immigration people when you stamped in you're NOT here on any type of visa, you're here on a visa exempt entry ;)
Also no matter what clueless websites on the inter-web state there are no more 15 day visa exempt entries by land for anyone :/ They were discontinued back on Dec 31st 2016. That's when they went back to 30 day visa exempt entries by land BUT put a limit of two by land in a calendar year (Jan 1 - Dec 31) for people from 44 countries.
When talking about visas/extensions etc it is very important to get the terminology correct. As you might surmise I am quite a stickler for correct terminology.
Sorry this was long, hopefully it is semi-useful
TLDR : Answer Summary
The discussion clarifies the differences between various types of visa entries into Thailand, emphasizing that there is no such thing as a '30-day tourist visa' or '30-day visa on arrival.' Instead, visitors who enter without pre-purchased visas are considered to have a 'visa exempt entry' applicable to certain countries. It explains the types of entries available, the extension policies for each entry type, and stresses the importance of accurate terminology regarding Thai immigration.
