Firstly store you "paid or not paid" value as bit in sql server.
when u retrieve that value, use as :
SqlConnection con = new SqlConnection("You connection string");
SqlDataAdapter da = new SqlDataAdapter("Your select query", con);
DataTable dt = new DataTable();
da.Fill(dt);
for (int i = 0; i < dt.Rows.Count; i++)
{
bool paid = Convert.ToBoolean(dt.Rows[i]["paid"]);
rdoPaid.Checked = paid;
rdoNotPaid.Checked = !rdoPaid.Checked;
}