Almost always, when available as a store option.
Even if it's an author I know and usually enjoy, if I haven't previously read the work in question, I'll want to try a sample of the text to make sure it's not one of their occasional duds before I buy.
And when possible I do also check the formatting on a previously-read book that I'm supplementing with a sale e-book copy, in case there's anything really messed up which would make it not worth spending even the modest $$$ which I could put towards a better-produced title.
Unknown-to-me authors have to pass a triple test of
- good sample on a promising-looking work I'm interested in
- good formatting on sample if downloadable
- good price and perception of value-for-money
There is basically no price threshold above "free" where I skip these steps for an unknown or only semi-trusted author. And even for "free", I'll turn down stuff if it looks like it'll just end up as poor-quality clutter on my hard drive that I'll never get to.
Incidentally, I'd advise putting the DRM-free info directly in the description which goes on the actual product page. It's the sort of thing some people want to know straightaway and it might work out better to tell them directly up front instead of sticking it in amidst some text that they just might skip past on the way to trying out the story.
Also, Sony seems to auto-DRM pretty much everything which goes through their system, whether it had any or not to begin with. IIRC, Cory Doctorow had to fight to get a special exception for his books to be made DRM-free in their store.