jqgrid: multiselect and disable check (conditional)

I love jqGrid but sometimes things seem more complicated than they should be.
What I would like to achieve is to have a checkbox on each row so that a user can choose which rows are going to be submitted/processed.
I need, though, to block some checkboxes cause the user has no authorization on that particular row, maybe.

I've tried to set multiselect: true and then I've tried to hide the checkbox:

loadComplete: function (data) {
    if (data.rows.length > 0) {
        for (var i = 0; i < data.rows.length; i++) {
            if (data.rows[i].cell[7] == 'false') {
                $("#jqg_OrdersGrid_" + data.rows[i].id).css("visibility", "hidden");
            }
        }
    }
},

and it works well but, still, .jqGrid('getGridParam', 'selarrrow') give me the selected rows, even if they haven't been checked.
Is there any other way to have checkboxes which are enabled/disabled and a way to know which ones have been checked?

thanks