Избавляемся от повторяющегося кода. Типовые решения

IAddress _address;
private void ChooseDeliveryAddress()
{
    using (var frm = new CatalogsForSelection.AgentDelivery.AgentDeliverySelect(_agent.ID))
    {
        if (frm.ShowDialog() == System.Windows.Forms.DialogResult.OK)
        {
            _address = frm.ReturnLastSelectedObject();
        }
    }
}

private IProductInStorage _product;
private void GoodsInStorageBrowse()
{
    using (var sForm = new GoodsInStorageSelection(1, _invoiceHeader.AgentID)) 
    {
        if (sForm.ShowDialog() == System.Windows.Forms.DialogResult.OK)
        {
            _product = sForm.ReturnObject();
            _accountPrice = GoodsInStorageAccessor.GetProductAccountPrice(_product.ProductID);
            FillProductData();
        }
    }
}

InvoiceHeaderByAgentBrowse retInvoice;
private void BrowseIncoming()
{
    using (var frm = new PRED2._0.CatalogsForSelection.InvoicesByAgent.InvoicesByAgentSelection(_invoiceHeader, InvoiceType.Incoming, false))
    {
        if (frm.ShowDialog() == System.Windows.Forms.DialogResult.OK)
        {
            retInvoice = frm.ReturnObject();
        }
    }
}

private void Foo(Form form, Action action)
{
    using (form)
    {
        if (form.ShowDialog() == System.Windows.Forms.DialogResult.OK)
        {
            action();
        }
    }
}
 
...
 
Foo(new GoodsInStorageSelection(1, _invoiceHeader.AgentID), 
    () => retInvoice = frm.ReturnObject());