a. (Please refer to the chapter on ribâ [usury] for a detailed discussion of the usurious sales.)

b. Gharar (undue risk taking): Gharar could be in the item sold (see section 2b below) or in the sale procedure. Gharar in the sale procedure includes sale by mere touching, mutual casting, or throwing stones. In these cases, people used to combine the sale with a gambling-like game. The sale would become binding if customers touched the sale item, tossed different sale items at one another, or threw a pebble at the merchandise and it fell on a particular item. (Note that Imam Ibn Taymiyah was of the view that all gharar is ultimately about the object of sale, not the process.)
c.  Ghabn (inequity), such as transactions under duress, those that involve cheating, and those with unequitable conditions.

2) Sale impermissible because of the item sold: a.       Inherently impermissible:                                       

i.  Useless                                     ii.     Has haram use only:

1.   Najis: e.g., khamr (wine), carcasses

2.   Not najis (e.g., idols)

b.   Haram to sell due to other factors:                                

i.  Gharar: non-existent, absent, unknown, unspecified, undeliverable items.

Imam an-Nawawi said in his commentary on Ṣaḥeeḥ Muslim:
“Countless types of sales are in this category [gharar in the item sold]. Examples of these would be: selling a runaway slave; selling items which are non-existent, unknown, undeliverable, or not fully owned by the seller; selling fish in a large body of water, milk in an udder, or a fetus in the womb; selling an undefined part of a heap of food or an undefined garment out of many… Some gharar may be tolerated for a need, as in the case of not being able to see the foundation of the building, or when one sells a goat with milk in its udder…, or the lining of a coat …”
ii.   Not owned by the seller:

1.   Wrongfully misappropriated, taken by force, stolen, and so on.

2.   Owned by someone other than the seller, his or her authorizer, or one in his or her custody.