Mention must be made at this site of the custom of burying a statue of St. Joseph in order to sell a home you place on the market.
The custom hearkens back at least to the great St. Teresa of Avila (A.D. 1515 - 1582), foundress of the Disalced Carmelite Order. As her Order spread, a new convent had to be built, and in order for a new convent to be built, land must be had. When the nuns found a particular piece of land that was perfect for their purposes, they also found that their coffers weren't full enough to purchase it, so they decided to ask the intercession of St. Joseph, burying medals imprinted with his likeness in the ground of the desired property as a sign of their prayers. It worked.
It also worked for Blessed Brother André Bessette, who was able to get the land on which he built the Shrine of St. Joseph of Mount Royal, in Montreal, Canada by praying to St. Joseph and burying a St. Joseph medal on the grounds of the future site as a sign of his prayers.
Now, both of these events deal with acquiring land, not selling it, and they deal with St. Joseph medals, not St. Joseph statues. Nonetheless, over time, the folk custom came to be for sellers of homes to bury a statue of St. Joseph as a sign of prayer asking to find a buyer and hasten the sale.
How it's done
Most commonly, a statue of St. Joseph is placed inside a protective cloth and buried upside-down in the front yard. People differ as to whether the statue should be upside-down or right side-up, and whether the yard should be the front yard or back yard, but worrying about such things is unecessary.
Then a prayer to St. Joseph is said. One popular version of a prayer for this purpose is:
Memento nostri, beate Ioseph, et tuae orationis suffragio apud tuum putativum Filium intercede; sed et beatissimam Virginem Sponsam tuam nobis propitiam redde, quae Mater est Eius, qui cum Patre et Spiritu Sancto vivit et regnat per infinita saecula saeculorum. Amen.
English version:
Be mindful of us, O Blessed Joseph, and intercede for us with thy foster-Son by the pleading of thy prayer: do thou, in like manner, render the blessed Virgin Mary, thy Spouse, gracious unto us, for she is the Mother of Him, Who with the Father and the Holy Ghost liveth and reigneth world without end. Amen.
When the house is sold, God and St. Joseph are thanked, the statue is dug up and given a place of honor in your new home, and you, of course, tell others about the power of St. Joseph's intercession.
Is this custom superstitious? It is if one doesn't believe in the intercession of Saints and the good of making outward signs of prayer. Given that two million St. Joseph home-selling kits (offsite, will open in new browser window) are sold each year -- even to Protestants and pagans -- I imagine that most people who practice this custom do superstitiously bury the statues for a sense of "luck" more than anything. But that doesn't make the practice bad in itself, not when it's done properly: with sincere prayer, giving St. Joseph a place of honor in your new home, and telling others of the wonders of this great Saint.