Selly is just a platform and there is nothing wrong with it , I am using it over 2 years now and always fast support and solution whenever any bug or problem arise . Selly is one of the best and trusted digital item selling platform in my opinion , the scam you mention its the scammers who open autobuy store and scam people that do not mean selly scammer , Selly is free to all to sign up and use and they also have Premium plan with some extra perk .

eBay has tons of scam sellers that don't mean eBay is scammer lol .