try using the str_replace function in the value of the form elements so that it is already converted before posting. For example:
change:
<input name="quoteref" type="hidden" id="quoteref" value="<?php echo $row_WADAcustomer_quotes['Quote_Ref']; ?>" />
to:
<input name="quoteref" type="hidden" id="quoteref" value="<?php echo str_replace('"', '"',$row_WADAcustomer_quotes['Quote_Ref']); ?>" />