During my years on etsy, I have had just about everything possible duplicated--including exact copies made of my profile (who copies an entire profile?) and even how I leave feedback or name my items. The quickest that someone has made a knock-off of an entire collage sheet is three hours.
At the beginning I would get pretty upset. Last year I must sheepishly admit I even sent the seller of the "October special" below (mine's on the left; hers on right) a snarky little convo saying that she hadn't quite gotten the copy right and that I would gladly send over the names of the fonts I had used if it would help.
(She no longer sells on etsy and her name is not attached, which is why I include this as my only example from someone else).
Recently though, two things happened that made me much more zen about the entire process. First, I came across a listing for someone else's butterfly ephemera collage sheet described as "a new take on a popular theme." You see, several years ago I created some sheets with vintage butterflies on postcards (both below are mine):In 2007-2008 these were some of my most popular items. Since then, more than 200 different variations of "butterflies on ephemera" have popped up from other sellers. Seeing something that I had originally created now identified as a "trend" or theme could have been very frustrating--but I actually had to laugh. By turning the idea of copying on its head, I can see my best postings as setting trends. If I add a collage sheet of vintage keys or a new size like 2.6 inch pocket mirrors, it's become almost a game for me to see how long it takes until someone else does the same. And if something doesn't get copied--was it not good enough? Should I push my ideas further?
Secondly--and I think this is probably the most important--I realized that copying doesn't work. Remember the etsy shop with the "October Special" I mentioned above? Initially her entire shop of 100+ items were near duplicates of mine. After I contacted her she started going in an entirely new direction--making her own, original designs. And guess what? Her sales went through the roof! Shoot!
So now when someone duplicates my items--even if it's 99% the same--I say nothing for very practical, business reasons. A shop full of knock-offs of other people's work has no creativity of their own and etsy buyers can sense that. Sure, they'll get a couple of sales, but the best shops constantly push themselves, always being innovative and trying to stay ahead with new ideas and new products. That in the end is what will pay off.
So when something you create is full-on copied, and responses such as "imitation is the sincerest form of flattery" and "who knows who really came up with the idea first?" seem flat--remember that at the end of the day your creativity has inspired others and that is what pays off in sales and customers who are looking for innovation. Push yourself further and don't worry about looking behind to see who is chasing you.