A person purchases an item without having seen it. This transaction is valid. However, once he sees the item, he has the right to return it or keep it. This is irrespective of whether there is any defect in the item or not. Even if the item is exactly as he had envisaged it to be, he still has the right to return it or keep it.
A person sold an item without even looking at it. This person who sells the item does not have the right to take it back after he sees it. Only the buyer has the right of returning an item after seeing it.
A hawker came selling peas. The top of the heap had all good quality peas. Upon seeing this, the buyer bought the entire basket of peas. However, the peas that were in the bottom of the heap were of an inferior quality. He still has the right to return them. However, if all the produce is of the same quality, it will be sufficient to see a few. Once he does this, he forfeits the right to return them irrespective of whether he sees all the produce or not.