Selling Islamically legal goods for illegal ones
Like selling something halal for wine, pork, dead animal’s meat or idols in return.
Sale by a city-dweller to a desert-dweller
The Prophet prohibited the city-dwellers from purchasing from the desert-dwellers. In another narration, city-dwellers were prohibited from purchasing merchandise from merchants before they reach the market-place. Here, the city-dwellers are people who the knowledge of the price whereas the merchants traveling from other places and the deser-dwellers are ignorant of the prevailing market prices. Availability of information here gives an unfair advantage to one party, which is discouraged in Islam. This prohibition is fundamentally important in an era where those who lack information are commonly taken advantage of.
Sale of grapes to a wine-maker
Though this sale meets all the requirements of a contract (the object sold, grapes, is halal) the sale contract is discouraged by the Hanafi and the Shafe’i jurists while it has been considered invalid and nugatory by the Malekis and the Hanbalis. This shows that if the halal object being sold is to be used in a haram manner, the sale of that halal object becomes haram as well. This also applies to sale of weapons during times of sedition and similar examples.
This refers to the seller artificially increasing the price in an auction by conspiring with a bidder who does not intend to buy but bids just to raise the price.
Two contracts in one
It is prohibited to bring together in one contract two transactions like sale and commission, partnership and exchanging and marriage, agricultural partnership and trade-labour partnership.
Sale contract with alien condition
Though there are a number of opinions on this, the general opinion seems to be that having an unrelated condition in a sale contract is highly discouraged. One example of an unrelated condition is the seller prohibiting the buyer from on-selling the merchandise purchased.
Source: Kharofa, 83-90.