The buyer can reject the goods for breach of a condition to be performed the seller for example.
If the seller delivers more goods than the quantity contracted for.
If the seller delivers less goods than the quantity contracted for.
If the seller delivers instalments contrary to the terms of the contract.
If the seller delivers goods mixed with those of a different description.
In such circumstances, the buyer incurs no liability and any price paid is irrecoverable. The buyer may lose the right to reject the goods:
If he has accepted the goods and given something in earnest to bind the contract.
If the duration if any prescribed the contract has lapsed
If no duration is prescribed the contract but reasonable time has lapsed.