If value in certain cell equals "Certain Text" echo "Text"

I'm trying to get this to echo a warning message when the cell contains a certain text like "0" or "N/A". It would work when there was no value entered in the first place, but I can't get it to echo when there is already a certain value. Any help would be great. Thanks!

<?php
                $listing = "$_POST[listing]";

                $sql = "SELECT open_house_attended FROM property_flyers WHERE street_property = '$listing' ";
                $result = $conn->query($sql);

                if ($result->num_rows > 0) {
                    // output data of each row
                    while($row = $result->fetch_assoc()) {
                    echo "</span><span class='report_bignumber'><br>".  $row["open_house_attended"]."</span>";
                    }
                } else {
                    echo "<br> ". $noresults . "</span>";
                }

            ?>