Try this..
For your first method...You have to set
$mailer->isHTML(true);
Reference : http://docs.joomla.org/Sending_email_from_extensions
For your second method...
Sendmail function :
sendMail($from, $fromname, $recipient, $subject, $body, $htmlmode=0, $cc=null, $bcc=null, $attachment=null, $replyto=null, $replytoname=null )
so your code should be
JFactory::getMailer()->sendMail($from,$fromname,$buyerEmail, $subject, $body,true);