A couple of sites I run are horribly slow. I wanted to blame the hosting company, but tests (e.g. loading the default theme) suggest that they are not to blame. I've used tools such as Pingdom's Website Speed Test, which lead me to suspect that the problem is the theme. For example, server wait time is 5.45 s just for the CSS file.
I was looking at the Synthesis blurb, which says "a site running a poorly implemented theme...is going to have performance issues that no hosting solution will fully solve."
Well I am stuck with the theme which is a premium theme and quite annoying since it cost $50. But my question is, when you are looking at a demo theme before buying, how can you tell if a theme is poorly implemented? Is is just a matter of using Pingdom, or are there other giveaways?