$search_options = array();

  if (isset($_GET['office_number'])) {
    if (!empty($_GET['office_number'])) {
      $search_options[] = '(ListOfficeMLSID='.$_GET['office_number'].')';
    }
  }
  if (isset($_GET['mls_number'])) {
    if (!empty($_GET['mls_number'])) {
      $search_options[] = '(MLSNumber='.$_GET['mls_number'].')';
    }
  }
  if (isset($_GET['status'])) {
    if (!empty($_GET['status'])) {
      $search_options[] = '(Status='.$_GET['status'].')';
    }
  }

  $options_separated = implode(",", $search_options);
  // print_r ($options_separated);
  $search = $rets->SearchQuery('Property','RESI',
    $options_separated, // This works. Querystring is ?office_number=001203&mls_number=&begin_date=&end_date=
    array(
        'Select' => 'Status,MLSNumber'
    ));


// OUTPUT //

46 Records found!
Array
(
    [Status] => Active
    [MLSNumber] => 9973908
)
Array
(
    [Status] => Active
    [MLSNumber] => 3644932
)
Array
(
    [Status] => Active
    [MLSNumber] => 7326558
)
Array
(
    [Status] => Active
    [MLSNumber] => 6300379
)
Array
(
    [Status] => Active
    [MLSNumber] => 9280950
)
Array
(
    [Status] => Active
    [MLSNumber] => 5937901
)
Array
(
    [Status] => Active
    [MLSNumber] => 9043031
)
Array
(
    [Status] => Active
    [MLSNumber] => 8704645
)
Array
(
    [Status] => Active
    [MLSNumber] => 7979640
)
Array
(
    [Status] => Active
    [MLSNumber] => 9961888
)
Array
(
    [Status] => Active
    [MLSNumber] => 4220240
)
Array
(
    [Status] => Active
    [MLSNumber] => 7479277
)
Array
(
    [Status] => Active
    [MLSNumber] => 8237518
)
Array
(
    [Status] => Active
    [MLSNumber] => 6303257
)
Array
(
    [Status] => Active
    [MLSNumber] => 5531064
)
Array
(
    [Status] => Pending - Taking Backups
    [MLSNumber] => 2769713
)
Array
(
    [Status] => Pending - Taking Backups
    [MLSNumber] => 1058701
)
Array
(
    [Status] => Pending - Taking Backups
    [MLSNumber] => 2850206
)
Array
(
    [Status] => Active
    [MLSNumber] => 6936956
)
Array
(
    [Status] => Active
    [MLSNumber] => 2888683
)
Array
(
    [Status] => Active
    [MLSNumber] => 7296296
)
Array
(
    [Status] => Active
    [MLSNumber] => 8692772
)
Array
(
    [Status] => Active
    [MLSNumber] => 3469001
)
Array
(
    [Status] => Active
    [MLSNumber] => 5183234
)
Array
(
    [Status] => Active
    [MLSNumber] => 1464339
)
Array
(
    [Status] => Active
    [MLSNumber] => 5084432
)
Array
(
    [Status] => Active
    [MLSNumber] => 6214716
)
Array
(
    [Status] => Pending - Taking Backups
    [MLSNumber] => 5026725
)
Array
(
    [Status] => Active
    [MLSNumber] => 2925019
)
Array
(
    [Status] => Active
    [MLSNumber] => 9038028
)
Array
(
    [Status] => Active
    [MLSNumber] => 6151277
)
Array
(
    [Status] => Pending - Taking Backups
    [MLSNumber] => 5919214
)
Array
(
    [Status] => Active
    [MLSNumber] => 1764394
)
Array
(
    [Status] => Pending - Taking Backups
    [MLSNumber] => 1335349
)
Array
(
    [Status] => Pending - Taking Backups
    [MLSNumber] => 7954866
)
Array
(
    [Status] => Active
    [MLSNumber] => 4348252
)
Array
(
    [Status] => Active
    [MLSNumber] => 3319234
)
Array
(
    [Status] => Active
    [MLSNumber] => 1312539
)
Array
(
    [Status] => Active
    [MLSNumber] => 6813803
)
Array
(
    [Status] => Active
    [MLSNumber] => 4434784
)
Array
(
    [Status] => Active
    [MLSNumber] => 7397527
)
Array
(
    [Status] => Active
    [MLSNumber] => 6636947
)
Array
(
    [Status] => Active
    [MLSNumber] => 1605176
)
Array
(
    [Status] => Active
    [MLSNumber] => 5648233
)
Array
(
    [Status] => Active
    [MLSNumber] => 9438701
)
Array
(
    [Status] => Active
    [MLSNumber] => 6888595
)