First, it needs to be clear what is being sold: the business and assets or the shares of the company. The liabilities of the vendor in regard to the purchaser will be different according to the nature of the sale.
It will be important to verify the legal and financial capacity of the purchaser. Before any pre-contractual negotiations are envisaged, a letter of confidentiality should be considered.
Post-sale, it will be important to monitor that the purchaser has carried out any formalities which ensue from the sale such as a change in directors appearing on the public company and commercial register.