This is an excellent idea. Some questions and observations: -For it to be sustainable, I believe you are looking at a business model in which either customer or vendor pays for your services. Have you tried both approaches? -How do you ensure the cups are returned? trust or you make people leave a returnable deposit? the later seems necessary when your project scales up. -Some vendors (more so the big chains) use the cups as an advertisement device when people carry their logo around. Although it defeats part of the purpose, you may want to consider adapting your cups to be able to accommodate a logo (an option would be a sleeve made of recycled cardboard). -You may be able to partner with non-vendors that can also collect the cups: kiosks, public transport operators, etc.
All the best with your idea and wishing you a big success!
Great idea! Few points to consider: -if I have to drive there to refill my containers, I may prefer it to be in a place where I can do some other things: gas station, supermarket, etc -will it refill certain quantity or I can specify what I want? The later would be preferred by user. -if it's my first time there, how can I get the recipient? It may interest the brand's to provide their own which looks equal to the standard. Brands use package as advertising (I see that shampoo at your home and I get it. Additionally some people may not want to look cheap by using an unbranded package.