The Anti-Corruption Organisation of Thailand (Act) secretary-general Mana Nimitmongkol on Sunday claimed he had learned of high-ranking position-buying in some ministries.
The positions were offered for 10-30 million baht on condition of particular projects being approved in the future, he wrote on his Facebook page.
"Some ministries have ordered departments as well as state enterprises under their authority to submit procurement plans valued at 100 million baht and over, and report on their progress from time to time," he wrote.
Mr Mana told the Bangkok Post that at the ministry where positions were offered for money, C10-C11 government officials were invited to a series of one-on-one meetings at a major hotel in Bangkok where negotiations took place.
He also wrote that an executive at a large fund under a ministry was asked to set up a new project so money from the fund could be used and potentially siphoned off.
The executive refused to comply and was then threatened with a transfer by a high-ranking minister. Mr Mana would not reveal the name of the ministry to protect his sources of information.
Mr Mana said decentralisation and restructuring of administrative power would be a way to reduce the motivation for, and likelihood of, corruption.
Moreover, the criteria for officials' promotions should be clear and transparent and made available to the public.
An anti-corruption activist who spoke to the Bangkok Post said the reshuffle season, before the end of September, is usually when positions are promised in exchange for favours.
The activist added that many high-ranking government officials who were transferred on the order of the now-defunct National Council for Peace and Order after being accused of corruption have regained their high positions in the post-election era.
In a separate development, activist Srisuwan Janya is demanding an anti-graft probe into an MP's possession of a piece of mythical rare metal, known as a lek lai, which scientists believed may be made of gallium, and which has been declared as having a value of at least 700 million baht.
Mr Srisuwan said he will ask the National Anti-Corruption Commission (NACC) today to look into the MP's declaration.
He said it must be established whether any accredited agency has certified the lek lai or set a median price for the object thought by believers to harbour magical properties.
The activist also wanted the commission to find out if the lek lai has ever been traded in an open market or whether any owner has paid tax on it.
He said the NACC must spell out clear and credible criteria for determining the value of lek lai to set a standard for MPs' asset declarations.
In his mandatory asset declaration to the NACC, Kathathep Techadetruangkul, the lone MP of the micro Palang Thai Rak Thai Party, said he owned assets worth 1.112 billion baht including a 700-million-baht lek lai, a maha lek lai (super lek lai) valued at 300 million baht and Buddha amulets produced by the famed Wat Rakang worth more than 100 million baht.
The list MP said he was given the lek lai by a villager who dug it out of the soil 20 years ago and believed it would bring the recipient good luck.
In less than a year of the lek lai having come into his possession, Mr Kathathep said his life took a turn for the better.
A person had offered to buy the lek lai from him for 700 million baht but he turned down the offer, he said.
NACC secretary-general Warawit Sukboon said the lek lai declaration would be something to keep a close watch on.
In principle, the NACC would look into whether the declared assets and liabilities existed and whether they were acquired legally.
He said the commission would need to establish whether the owner derived the value of the lek lai based on intrinsic or sentimental value.
Mr Warawit, however, declined to comment on rumours that a lek lai valuation loophole could be used to launder money.
The anti-corruption activist, who spoke to this paper on both issues, said there had also been cases in the past where "prices were set up as a hint of tea money which the person would like to have. Anybody who wanted to bribe him would give him this amount of money and get the amulet in return.
"I wonder whether the NACC officials will have enough time to examine the assets of every politician who submits a declaration.
"There are over 7,000 local administrative organisations and at least 10 from each agency have to declare their assets."
Meanwhile, Weerachai Phutthawong, a chemistry lecturer at Kasetsart University, said the lek lai could be gallium worth some 10,000 baht a kilogramme, or also lead, which is sold for about 10 baht a kilogramme. He said the MP would be most welcome to submit the lek lai for lab test.