I've come down a long and hard road of trying to make WPEC work with several of the blog themes available at WP.org with only minimal success enjoyed until the next upgrade of WPEC. While I have seen excellent implementations of WPEC, none were in blog themes. My results with the 2012 theme were awful, and in all fairness to WPEC developers, this probably wasn't their fault. My conclusion is if anyone wants to run this, they should consider purchasing a theme made to run it.
Now, about support - it doesn't appear to exist. So if you think you will get all straightened out by purchasing Gold-Cart, you are wrong. If you want to give them 40 bucks, do it for the sake of supporting independent software authors. For me there weren't any features in it worth paying for, but I did anyway.
WPEC is fairly simple to use, and fairly flexible. I found the included shipping options to be rather lackluster but adequate with an additional plugin.
Don't expect you will set up an e-commerce site for nothing. It is likely you will have to buy some functionality not included unless you know how to make it, but WPEC extensions tend to be affordable.