I bought a brand new one a few months ago after seeing that the used ones were almost the same price. The trigger does take some getting used to, but its a very reliable trouble free platform.

Its a great entry level pistol at a great price from a reputable manufacturer. The low price creates a lot of interest and sales and S&W is making a ton of them.

Folks are simply moving on to a better pistol (like the M&P series) rather than modifying the SD with after market parts. This is probably why you're seeing so many used ones for sale - not a defect in the pistol at all. Should you decide to modify the SD, you'll be pretty much be in M&P country pricewise. If you buy it and use it as a self defense pistol to be used as a last resort. its great!