In the case of a product purchased from an individual, then the Spanish Civil Code is where the governing law is to be found since the law does not consider the transaction to be carried-out by a consumer, but rather to be a transaction between to equal individuals. It should be noted however, in the case of a professional seller, the matter may be dealt with by the Consumer Protection Act.
This means that should there be any complaint relating to a product purchased second-hand from another individual, it must be made within six months from the date of purchase.
In addition, the remedies available are reduced to either product repair or reduction in price/return of the purchase monies i.e. the purchaser may not demand substitution.