I include a business card with every shipment, along with a coupon for 15% their next order. i hope people at least save the coupon. But I kind of doubt it , because I think about 5 people have used it in 2 years. Honestly, I don't always keep my cards either, unless its another I meet in person at a craft fair, that I might want to network with in the future. I toss them, knowing if I want to come back to their shop I can find them online.
However, if I got sent a coupon that never expired, I would definitely keep it, especially if it was from a shop I liked. I'm thinking about condensing my business cards with the coupon. OR, perhaps using a stamp, and stamping the back of my business card with the coupon code and a message. For environmental factors. People respect that alot too.
In fact before I sent coupons separately, I just stamped them into the thank you card. But no body ever used it. So, maybe I will, like I said above use the stamp on my business card.
These day everyone is so technologically reliant that when I'm looking for the shop i last bought something from, the last thing I want to do is go digging through my junk drawer for their coupon/or card. So thankfully, ebay and etsy save everything.
Also Recently I started offering 20% off coupons to people that come back and leave me positive feedback. Because, I know, from personal experience, i can be lazy about doing it, but having an incentive makes it worth while. So, actually of all the coupons I have given out, that one is the most popular, and it reminds people to come back and leave me feedback.
Also, I hand my cards out regularly to people I meet on the streets that like my jewelry, or bring them to craft shows.