Many of my clients have purchased SUPERAntiSpyware via the superantispyware.com site and I've never heard any negative comments about the site. A few have actually mentioned that the site had a clean, professional, and legit look/feel. No pop ups, annoying banners, etc. I think the site is very easy to navigate and makes buying the product simple (which is the main reason I direct customers to the site).
One area that could use a little work is the cart / checkout. It works perfectly and the information is clear and concise, but the up sell options (adding the lifetime subscription and additional copies) don't really grab your attention. Maybe add box art imagery or something that draws people to purchase the "add ons".