It might be the case that people are just tinkering with this service for fun, but the "yay, unexpected socks" use case seems like a solved problem with Amazon

It might be the case that people are just tinkering with this service for fun, but the "yay, unexpected socks" use case seems like a solved problem with Amazon Subscribe and Save lists (http://www.amazon.com/Subscribe/b/?_encoding=UTF8&camp=1789&creative=390957&linkCode=ur2&node=979895011&pf_rd_i=subscribe%20and%20save&pf_rd_m=ATVPDKIKX0DER&pf_rd_p=1542108682&pf_rd_r=2FB7714E2588456CAAE1&pf_rd_s=auto-sparkle&pf_rd_t=301&tag=books07059-20 http://www.amazon.com/Subscribe/b/?_encoding=UTF8&camp=1789&...). To each their own, but I just don't see myself reinventing the wheel with this API (not to mention paying an additional 5%) to buy socks/paper towels, when Amazon has already done that leg work for me. I do, however, agree with meritt's sentiment above...zinc.io could be used to create some valuable services for existing businesses (rewards programs, et al), but as a user of this API, I think it'd be much more cost effective as a fixed per-order fee structure.