You can just ask the Etsy shop owner. I've contacted people selling my designs on Etsy before to ask where they got the artwork, and all of them have been very open about it. Many offer to remove the products before I even ask.

The problem with Etsy is that not every stock companies regards it the same. Most stock licenses prohibit use in print-on-demand situations like Cafe Press and Zazzle, but some stock companies view Etsy as more of a retailer, since some products are one-off products.

But in the case of stock image use, they are really almost always print-on-demand and shouldn't be allowed under most regular licenses or even ELs.

Thank you, EmberMike, for your answer. I've contacted the shop owner and, just like you said, he took down those items before asking. I just asked which licence he bought and from which site. The answer was ambiguous, something about someone sold him the vector on Etsy (!!!) Anyways, I think he had no licence at all, but I am glad he took those prints down.

Often when someone doesn't have a license they'll immediately remove the products. You don't have to even send a threatening email, just a polite mention of the image and inquiring about which stock site they bought it from often scares them into removing the unlicensed products.

When someone does think they have a legit license, they'll tell you. And even then sometimes they'll offer to remove the product before you ask.

The only stock agency I know of that allows Etsy product use is iClipart. And even then I wasn't sure and had to contact them to find out if the license covered it.