What is the ruling on a group of individuals agreeing not to bid against each other in a public auction, then selling what they purchased and dividing the amount among themselves?

If there are others in the market besides them, it is not permissible to agree to prevent anyone from entering the auction. However, if there are no others in the market besides them, there is no harm, provided they do not prevent anyone from entering the auction. If they prevent someone from entering and agree with him that he should be a partner in the profit, then it is not permissible. And if they give him a sum of money, he must return it or give it in charity.