You obviously don't network in the ecommerce very well, and your manner definitely suggests that. I can give you dozens of articles that show custom themes are not all that.
heres on example:
and you obviously have no idea on how websites work if you're giving every website a one-size fits all packages (pre-built theme).
Yes they are cheaper but there comes a lot of risks e.g.
- the website isn't branded to you (on more than one occassion I have noticed 2 websites that use the same theme but are competitors).
- the pre-built theme is built to fit one solution, they tend not to be customisable to fit alternative solutions.
- the person installing the theme has no idea what they are doing and they then blame the theme / author for being poor when it's not been setup right.
Magento is a pain in the ass system, if you don't set it up right for your needs, it will literally break down and need major work to get it going again.
I use pre-built themes for clients on tight budgets but they still get my experience and support setting it up, most people who buy themes won't have that support and will ultimately mess it up. If the OP was to use a pre-built theme and then use Zigo to build the site then it would be a great site, but if the OP wanted to do it themselves then more than likely it will go wrong.
I am generalising here and there is a reason for it, 99% of people have no clue how a website works, how their visitors expect their website to work. They see 2 costs £10k from a developer and £200 from a theme marketplace, which looks more appealing?
I take my car to the mechanic for my MOT and to fix any issues, why are businesses so tight when doing the same for their website? It's not a toy, it's their business and they are trying to cut corners which will ultimately end up in the business going bust because they didn't have a clue what they were doing.
I build & sell pre-built themes as well as build custom themes and the worst clients are those buying the themes, they pay upto £200 for a theme but they expect me to build their website for them and work for them on any issues. My freelance clients give me no hassles what so ever as they are paying me a decent wage to do the job properly.
Pre-built themes are great for getting started on a budget but you still need to factor in using a developer who knows what they are doing otherwise it will all go wrong. In 99% of cases, the business owner is better spending the time for a custom site so they get the support they need.