I need to make myself a macro, since I'm going to say something very like what I said to someone else in the last week.
I see from the links in your signature that you have already released "The Killer Contract Agency" on Smashwords, although it's no longer available. Seems like the time to get a beta read and make whatever changes would improve the work would be before it's put up for sale.
You've presumably had people buy it, in what will be an inferior version if you get beta readers and make changes based on their input. Even if you offer a free download to earlier buyers (or free downloaders), how will they know to seek that from you?
Instead, I'd recommend getting the input on a manuscript you have not yet released into the wild.
Maryn