Found this interesting ThaiVisa article on Baht-Stop about foreigners working in Thailand.

It's from a seminar where officials from the local labour office were interviewed over when and under what circumstances work permits were required by foreigners.

It's interesting but some of it still sounds vague...

From: http://www.thaivisa.com/forum/topic/473 ... ent-talks/

This is the legal definition of work they use:
the legal definition of work that is used by the Labor Department; "to engage in work by exerting energy or using knowledge whether or not in consideration of wages or other benefits".

Additionally Khun Rhuchuchai pointed out that beyond the application, is the intent. If itтАЩs clear there is intent to work with a goal to profit from that labor, either on the part of the foreigner or of the business, then that is also illegal.
This seems to take care of establishments like The Venue who get overseas performers in sometimes:
A key question that was asked was in regard to performers who wish to perform a one off show for charity or otherwise. He said there is a temporary permit to work for not longer than 15 days, free from his office and considered on a case by case basis. But, he pointed out several times, you must apply for it. He reiterated that he supports those who wish to perform legally, and will be happy to approve such applications for these kinds of shows once applied for and considered on a case by case basis. Anything over the 15 days requires a legal work permit, which requires a sponsoring business or charitable organization.
Volunteer work:
Volunteer work, he pointed out, requires a work permit, however, many charities are looking for volunteers and are willing to sponsor people and he suggested that he could offer guidance to those interested in such a work permit. For those who wish to work at multiple organizations, he pointed out that that initial work permit is required but it is possible to add an employer or job to the work permit once its issued. This would also apply to musicians who wish to play at different venues.

He noted that the office offers different periods of work permits, from a year for 3,100 baht to 6 months for 1,550 baht and 1-3 months for 750 baht.
Freelance work (some posters on ThaiVisa dispute this):
He added that there is no тАЬfreelanceтАЭ work permit, that one must be sponsored by a company.
This seems to allude to "specialists offering advice for overseas clients in overseas markets":
when asked about specialists offering advice for overseas clients in overseas markets, he felt that so long as they did not offer that advice to Thais or foreigners in Thailand that would be acceptable.
This is interesting. When I visit Thailand, I usually continue managing the work of my staff (in Australia) and doing work for Australian clients. I do this remotely, from my laptop. I don't think this is much different from thousands of other executives who action their e-mails and keep in touch with their office while holidaying in Thailand.

It brings up a few questions...

Can I assume he's referring to specialists located INSIDE Thailand "offering advice for overseas clients" or is that incorrect?

What is the significance of the specific wording "offering advice". Advisory is part of what I do for clients but there's a lot of document generation and such too. Does the policy he describes distinguish between the two or does it refer to any sort of knowledge work?

I wonder if his comment basically applies for any tourists who does work for overseas clients (no involvement of local labour or local clients whatsoever) while in Thailand. Where is the line drawn?

I'm not too bothered as I'm only ever in Thailand for short periods of time - sometimes less than week, occasionally up to 2-3 weeks - but it's nice to know where you stand.

I'm guessing this is what small businesses do:
A company started by a Thai person and employing and paying social security for 4 Thai employees can offer one work permit for a foreigner without needing the required 2 million baht in registered capital.
Read all: http://www.thaivisa.com/forum/topic/473 ... ent-talks/