As I understand it if you get a regular ‘visa on arrival’ at the airport or a border crossing (after paying your 500 Baht penalty supposedly to cover potentially unpaid medical bills) – however long that covers you for (used to be 30 days I think) you can seemingly exit Thailand and return three times in a row max. If that is correct, and these things do change quite often with no particula logic, that would give you theoretically three times 30 days which is probably max in any one 12 month period. Correct me if I’m wrong.
Other types of visa are also available for longer stays but usually need to be applied for in your home country and do not allow ins and outs. These include, or used to, something called a ‘retirement’ or ‘retreat’ visa – presunmably in case you want to become a tempoary monk – which was good for a year in Thailand – but no in and out.
Mostly these ever shifting visa restrictions are aimed at making life difficult for foreigners who come in on tourist visas and then work, for example such as yoga teachers and baristas. Of course, slave labour involving poverty stricken Burmees and other SE Asians in the shrimp business goes on, as one might expect. However, interestingly during my time in the ajacent Lao capital, Vientiane, working western expats, which included the likes of World Bank and UN emplyees as well as other NGOs and lowly ESL
teachers, were always eager to spend their weekends in Bangkok. Then the Thais, as now, suddenly decided to change the visa rules restricting the number of times you could come and go a tourist visa. This apparently brought about an official complaint from the afore mentioned institutions in Vientiane and low and behold things quickly went back to normal. So it often depends on who you are. Nevertheless, generally visas in Asia, and unfortunately elsewhere too, are becoming more and more restrictive and expensive which really kills the entire notion of anything approaching real travel as we knew it It’s just a business..