The best response is to refund these people and block them from communicating with you further. If you make the mistake of engaging a troll, you might be dragged into a "flame war." Like bullies, trolls get their "juice" from the conflict. Refuse to go further. Report the troll to his ISP and block him from all further communications with you and your business.
As you can see, reputation management isn't as straightforward as it seems. There are many online predators and criminals who can wreak a great deal of havoc for you and your business. As mentioned earlier, your best defense is to build a strong business presence online. That, combined with excellent customer service, will help you over the short and long term.
Nathan Segal has been working as a freelance writer based in British Columbia, Canada. Reach him via email or visit his website. Follow everything from CIO.com on Twitter @CIOonline, on Facebook, and on Google +.
Read more about internet in CIO's Internet Drilldown.