A verbal agreement will stand in a civil court for as long as you can prove it. Verbal agreements are difficult to enforce in that they are difficult to prove. However, the party who dishonours the agreement may have acted in a way which could amount to an irrefutable presumption that the agreement had taken place. Non-written agreements are to be discouraged even between friends, because not only they are likely to create tensions and eventually destroy the business relationship, but also do away with frienship.
This applies to Spain as much as to any civilized country.
