The transfer of shares can take place in any form, as the written form is not required. The formal requirement associated with such transactions in practice - i.e. notarization - is not relevant for the validity of the transfer of the shares, but for the entry of the transfer in the commercial register.
In the case decided by the court, the owners of the shares had sold them by signing a written contract. When the agreed price was not paid, they sued the acquirers and requested that they be ordered to pay. The court upheld the sellers' claim and rightly clarified that the transfer of a share in a S.r.l (Ltd) is not subject to any formal requirements; the written form is not even necessary for the validity of such a contract.
As a rule, it is in the interests of the parties involved that the transfer of the shareholding is enforceable against the company, so it is always advisable to make the transfer in the form of a public or notarized private deed.
In Germany, the legal situation is different, as the assignment of GmbH-shares must be notarised in accordance with Section 15 (3) GmbHG.