well i would go to a good violin maker someone who knows their violinst or a historian to maker sure that it is a stradivarious.
But seriously why would you want to sell it those thing are rare as hens teeth and are worth a fortune!!
if i were you i would keep it but i guess if you need the money then you could sell it but there worth f&^*ing shitloades

Stradivarius violins are known for being extremely famous and expensive as well. A Stradivarius violin made during the time period in which Antonio Stradivari lived is believed to be the most famous and expensive violins. If the violin was produced in the 1680’s, it could be worth more than hundreds of thousands of dollars today, if it were to be sold. If a violin was produced during the period between the early 1700’s up until 1720, otherwise known as the “golden period,” and the violin is in good condition, it is sold at very high prices. A violin produced during this period can be priced at over millions of dollars. Not many Stradivarius violins are sold however, for many of them are owned today by either musicians, or organizations and foundations such as the Stradivari Society. The highest price that a Stradivarius was sold for was $3,544,000, but this was merely the highest price bought at a public auction. The bidder’s was reported to be anonymous. This violin was called the Hammer, and was produced during the golden period, in the year 1707. Before it was sold at over three million dollars, the violin’s price was estimated to be no less than 1.5 million, and no more than 2.5 million dollars. But on May 16, 2006, the bidder bought the violin, and the bid was recorded into history as the highest price an individual has ever paid for the Stradivarius violin at a public auction. Private sales of Stradivarius violins have exceeded this price, however, so the Hammer remains merely the highest priced violin sold at a public sale.