What is the name of your state (only U.S. law)? New York
can I sue/should I sue for roughly $300 that someone owes me? They agreed to sell me a product and when I paid they didn't deliver?
Is the product you purchased a "legal" product (i.e., not drugs or stolen goods)?
If so, then you can sue.* Only you can determine if it is worth your time and effort to do so, though.
Good luck.
*and you can sue if the goods were illegal, too - it just tends not to be a smart thing to do