Reselling online will be a good business, but you have to think about what will you resell. Will it expire in one or two-years time? Is your product on the top sales of most online shop apps? You should consider such things, because this may impact your sales as well as your rating as a seller.
I have a friend who is doing reselling clothes. At first, her business was a success, but after 6 months, buyers are slowly decreasing. I haven't asked her the cause, but maybe it is because there is nothing new product to offer her customers.
Therefore, before you jump in to online reselling, study thoroughly what you will you resell and who are your target customers.