I can definitely understand the frustration, but Google won't penalize sites for simply having duplicate content, and especially storefronts. Many merchants are provided with photos and product descriptions by the distributor, and when you're talking about hundreds or even thousands of products, it just not feasible for a merchant to change all of the descriptions and even more so if your inventory is changing on a monthly or even weekly basis. Then all of your changes get overwritten with the new upload.
A good example would be the SMC websites that you see on late night TV where they send out a CD with products to thousands of customers and 98% of them just upload the database into their stores with little to no alteration. They won't be penalized, but they just won't be able to sell much.
In those cases, the sites aren't going to be penalized. And if those sites are ranking well without changing the content, then Google is definitely looking at other factors to make that decision (traffic, bounce rate, time on site, etc.).
The sites Google are penalizing are the ones that intentionally try to game the system by stripping content from other sites and reposting them with literally no changes at all. Also sites that try to duplicate one of their stores multiple times in a cookie cutter fashion in order to trick the system to see if they can get multiple listings on the SERPs.
You haven't provided specific sites to review for a definitive answer here, but they don't sound like they're trying to do anything black hat. They're just lazy. But if your site will be selling the same products, altering your descriptions and images is the only way that you'll get the advanatage over them instead of just becoming "yet another one of those sites". Good luck!