Since it is forbidden to have hametz during Pesah in some communities it is customary to sell the hametz to a non-Jew through the local rabbinate. This is the way this selling is done: the community member signs a paper (virtually, a power of attorney) authorizing a Rabbi to sell his hametz to a gentile. The rabbi sells the hametz to a non-Jew Pesah eve. The buyer gives a down payment for the hametz to the rabbi and commits to pay the balance up to a few minutes after Pesach is over. During Pesah, then, the buyer is the legal owner of the hametz, even if the hametz still remains in the property of the Jewish seller. When the buyer fails to cancel the balance (although, if he wishes to do so, he can theoretically and legally pay the balance and collect his hametz!), immediately after Pesach, the hametz belongs back to the seller.
Until recent times in Sephardic communities it was not customary to sell the hametz to a gentile except in exceptional case, e.g., someone who owned a food store. Traditionally, Sephardic Jews got rid of all their hametz (bi'ur hametz) as prescribed by the Rabbis of the Talmud, and if some hametz accidentally had not being detected, then the bitul hametz,i.e., renouncing to our ownership of any undetected hametz in our possession, would prevent the transgression of owning hametz during Pesah. If we take these two simple steps, then there is no need to sell any hametz. Whenever possible this is the best way to proceed and to preserve the ancient Sephardic Minhag. (This is, by the way, what I have been doing for years. I personally avoid keeping any hametz at home and selling it...). Remember that you only have to get rid of hametz which is afood item (for pets food, see note below). Medicines, perfumes or any non edible items could be kept, regardless of its composition. Food items: you could keep anything as long as you make sure that it does not contain any of these five grains: wheat, barley, oats, rye, spelt (FYI, anything which contains gluten, is hametz. Check online!). All those community members who wish to continue with the tradition of removing all hametz from your premises and avoid the selling of the hametz, can email me (email@example.com) a list of food you wish to keep and I will email back the status of that food (K: Keep. D: Discard or give as a gift to a non Jew)
For those community members who wish to keep their valuable hametz products (whiskey, vodka or liquors made from grain alcohol, etc), in order to avoid transgressing the prohibition of owning hametz during Pesach, there are many ways to arrange the selling of the hametz thru the local rabbinates. You can also email me.
Pet's food are usually hametz and it is forbidden to use them for your pets or even to keep them during Pesah. For a list of Kosher lePesah pet's food see HERE