Things I looked for......... A solid beefy construction, plenty of available headroom to handle even the most demanding movie segments, and effortlessly capable of hitting the deepest of notes. Pure physics dictates how low a sub can go, and there is no substitute for the "beefy" construction necessary to accomplish those ends. For a sub to do it's job well, it literally needs to be built like a tank.
Free shipping?? For me, that means little. Shipping cost is a minimal factor when looking at the total cost.
Bundling?? Just how many subwoofers do you plan to buy?

Most people use only 1 or 2 in their HT, and that's not nearly enough to warrant a bulk discount.
Sacrifices?? Some will sacrifice performance due to space restrictions requiring them to buy a smaller sub than they may otherwise like to purchase.