Selling your chametz before Pesach is not a trick, but a legally binding sale. When you sell your chametz it belongs to the buyer who has every right to use it.
In a certain community, all the chametz -- including the kosher pizza shop -- was sold to a police officer. During Pesach, a burglar broke in to the pizza shop. The policeman, who happened to be on duty at the time, entered the pizza shop, arrested the robber, and exclaimed, "You're robbing MY business!"
And it's told of a whiskey producer in Europe who sold his entire business for Pesach. After Pesach, the buyer decided he wanted to own the business permanently, and so he refused to sell it back.
But you're right. Both buyer and seller should take the sale seriously and realize that it's not a 'trick.' I know of a Rabbi who, in order to show his congregants that the sale is no joke, told the buyer to enter a home during Pesach and ask for his chametz!
Sources:
Shulchan Aruch OrachChaim 448:3
