I have to purchase a patent by a private person in order to produce it in my company. How can I be sure of its validity? Is it sufficient to have a declaration of this released by the inventor?

Before purchasing a patent it would be wise to do the necessary verification, as a simple declaration given by the inventor is of very small importance. Of course this could be useful to act against him in case of bad faith or false information, but it would not resolve the risk of being unable to use the patent and having to passively accept any eventual infringement by third parties. Quite often, unfortunately, it has happened that the same inventor is convinced of the validity of his own patent and is unaware that there have been certain factors invalidating it or, in fact, it has never had any value. The first thing to be done, as soon as you have the details of the patent to be purchased, is to make a formal check to establish that it has in fact been granted, that the fees maintaining the validity have been paid and that the likely transferrals of ownership have been registered. After this, it will be necessary to do a search for novelty, as, even if it was granted and from the formal point of view all is in order, this does not rule out that there could be an identical patent of a prior date, as the Minister does not do any search in this direction. The novelty search and analysis of it must be done by a competent consultant who can interpret it according to the patent you want to purchase, therefore he can also supply a proper opinion to the specific matter. If all these give a good result, then you could purchase the patent without any concern; on the contrary, or by not doing any of the above, you risk throwing away money and energies.