Contractual expert determination, being configured as a collective mandate whereby the parties refer to one or more third parties the task of formulating a technical assessment whilst undertaking in advance to accept the proposed solution, is not susceptible to challenge for nullity under art. 828 Code of Civil Procedure, remaining challengeable exclusively for defects that may affect any manifestation of contractual will, such as mistake, fraud, duress or incapacity of the parties.
In contractual expert determination, the provisions of art. 1726 Civil Code applying as collective mandate, revocation effected by only one of the mandators does not produce effects, unless just cause exists, in which case termination occurs in respect of all mandators.
Contractual expert determination, implying recourse to technical norms and technical-scientific criteria proper to the specific competence of the expert, is not susceptible to challenge through the protection provided by art. 1349 Civil Code for arbitraggio, which differently presupposes recourse to objective criteria of mercantile equity for the balancing of the parties' interests.
In contractual expert determination the essential mistake relevant as a cause of annulment must present the requirements of essentiality and recognisability under arts. 1428 and 1429 Civil Code and must vitiate the process of formation of the experts' will through a false representation of reality, excluding the possibility of asserting errors of judgment or interpretation of law.
Any erroneous interpretation and application of a rule of judgment established by the parties in contractual expert determination may be traced to the concept of abuse of mandate constituting a source of liability for the experts, but does not constitute reviewable mistake nor cause of ineffectiveness of the determination.