bool result = false;
for (int i = 0; i < TalepSatirlari.Content.Rows.Count; i++)
{
    double satirtutari = Convert.ToDouble(TalepSatirlari.GetValue(TalepSatirlari_Columns.SubTotal, i));
    if (KullaniciLimit.Value.Value >= satirtutari)
    {
        result = true;
        ShowMessage("result true ise", result.ToString(), MessageType.Information);
        break;
    }
}

return result;