4. Sales on approval. A sale on approval is a sale made on condition that the buyer shall have the opportunity to examine the property and decide whether to take it or reject it. The period of time for examination will be fixed by the seller. In sale on approval, it is assumed that the buyer has to buy in following cases:
a. if the buyer does not notify his refusal within the time fixed by the contract, or notice, or usage.
b. If the buyer does not return the property within the time,
c. If the buyer pays the price or part of it,
d. If the buyer disposes of the property or does any other act from which acceptance may be implied.