I don't know about printable coupons, but I bought a bunch of Lowe's coupons from eBay last year. Excuse me, that's not true: I bought a plain white envelope, and it just happened to contain the gift of several coupons.
It was well worth the $3 that I spent on the coupons. I saved 10% off the already-on-sale dishwasher, stove, range top, and installation. I compared everywhere before making that major purchase, and for the middle-of-the-line, energy-efficient products I wanted to buy, Lowe's was the best deal.