The main difference between sale and agreement to sell is that when the buyer takes delivery of the goods, it is a sale. However, an agreement to sell is an intention to create legal relations between the seller and the buyer.
In other words, when the seller agrees with the buyer to sell something in future and there is a contract between both parties, it becomes an agreement to sell. On the other hand, a sale takes place when the seller transfers ownership of his/her property for a price.
However, an agreement to sell is when a seller agrees to sell his goods on certain terms and conditions, with the buyer getting no right over the goods until the conditions are met. The sale of goods, on the other hand, is when a seller transfers his ownership of goods to the buyer for a consideration, which puts an end to the ownership of the seller.
In agreement to sell, the seller has a right to retain possession of the goods until certain conditions are met, as he would in any contract for the sale of movable property. The buyer has no rights over the property in this case and cannot take possession of it unless all conditions are met.
Sale, however, is a transfer of ownership from one person to another for money or money’s worth. Once sold, title passes from that moment itself and the buyer can have possession and claim ownership immediately after purchase.