After installing Zen Cart or any other shopping cart software for that matter one of the first things people usually do is to try to customise the look and feel of the site. Most people don't have the the design skills, technical know how or the time to make their own templates so they go looking on the net for either someone to create a custom one for them or to buy a pre made one. If you look for long enough, you will inevitably come across a company called Template Monster. This company has a notorious record for producing very badly coded templates, some of them may look fantastic but it is what's hidden beneath the glossy exterior that matters. I've come across numerous people and read many, many accounts of store owners who've had nothing but trouble trying to use one of Template Monster's templates.
Even some Zen Cart developers have requested that Template Monster withdraw some of their templates, yet months later they are still selling them despite numerous complaints about them. For $150+ each you'd expect more for you money. Don't let their flashy graphics fool you, ask yourself if it's worth paying that sort of money for something that could make your store only semi functional. I could go on all night telling you about some of the problems I've come across with Template Monster's templates in the past but I'll only be repeating what many others have already said. Don't take my word for it, read for yourself what others have said about Template Monster.
http://www.zen-cart.com/forum/showthread.php?t=56585
http://www.zen-cart.com/forum/showth...mplate+monster
http://www.zen-cart.com/forum/showth...mplate+monster
http://www.zen-cart.com/forum/showth...mplate+monster
http://www.zen-cart.com/forum/showth...mplate+monster
http://www.zen-cart.com/forum/showth...mplate+monster
Just to show that it's not only Zen templates that are affected, here's a couple of examples of osCommerce users who've also had problems with Template Monster.
http://forums.oscommerce.com/index.php?showtopic=253152
http://forums.oscommerce.com/index.php?showtopic=277953
It should also be noted that when reading reviews on some of the "review" sites that many of them are far from unbiased. Much of what they say should be taking with a large pinch of salt. To gauge what a company's services or products are really like in the real world it's often better to check out the industry's forums and read what "real" users have to say on the subject.