Mr Guest, also a Dunedin city councillor, has denied venturing into prohibited areas through his involvement with the site, saying the website, separation-international.com was his brother's and nothing to do with him.
Mr Guest was struck off in 2001 for professional misconduct, and, despite reinstatement to the High Court's roll last year, is yet to regain a practising certificate.
Without the certificate, some types of work in reserved areas are off-limits to Mr Guest.
The website offered its customers separation agreements available for download and tailored for use in seven countries, including New Zealand, as well as tips and information on practice and procedure.
New Zealand Law Society vice-president Anne Stevens, of Dunedin, said the website appeared to be above board, but Mr Guest's involvement came "so close" to venturing into prohibited areas.
She had forwarded details to the society's national office, and expected an opinion within days.
"Once people separate, you are going to get so into stuff that's reserved work ... relationship property agreements you want to file in court [and] parenting issues.
"At the moment, on the face of it, it's not a reserved area of work - but it's so close," she said.
Domain information showed the website was registered to Mr Guest's home in Opoho, with his email address, street address and phone number shown.
However, the name of the person who registered it was listed as Mr Guest's brother, Andrew, a lawyer based in Auckland.
The site was registered in August 2008, and due to expire today, unless renewed.
Mr Guest said when contacted yesterday he was aware his brother had started the site, but was surprised other details linked it to him.
"There's been a mistake, but it's nothing to do with me," he insisted.
"I'm not running a website which gives legal advice."
Later yesterday, in an email to the Otago Daily Times, he clarified he "came up with the idea" for the website more than a year ago and helped design it, but was not involved in its operation.
"I have never received any money, directly or indirectly from it. No money is owed to me for it."
The site offered separation agreements for purchase and download, but was "static" with no interaction between customers and the site's operator that could be misconstrued as a lawyer-client relationship, he said.
He was quite clear about the areas in which he was restricted from working, and "I'm not doing that. I am quite within my rights to have some limited involvement with the website.
"Not one of the reserved areas of work is touched upon by the Separation International website.
"The website gives no advice about actual or contemplated court proceedings. An agreement is a world away from a court proceeding," he said.
Mr Guest, a former district court judge, was struck off in 2001 for professional misconduct, but reinstated to the High Court's roll of barristers and solicitors in October last year.
However, a New Zealand Law Society decision not to issue Mr Guest with a practising certificate was upheld last month by the Lawyers and Conveyancers Disciplinary Tribunal, which released a heavily abridged decision.
Further details were withheld pending any submissions or an appeal, with the deadline last Friday.
A Ministry of Justice spokeswoman, contacted on Friday, and again this week, would not confirm whether an appeal or submissions had been received, saying only a decision would be released "once it is available".
