I have two kids who are a bit more than four years apart, and we've been through all sorts of strollers. Singles, doubles, umbrella strollers, joggers, and so on. Of the six or so strollers we used heavily, only one broke down before the or kids outgrew it. Some we gifted on, some we keep just because who knows, and a few we have sold for a decent profit.
If you do some research and find the most popular new strollers, you can then search out used units for sale on the cheap. Posting them at a markup can make you handy cash, especially when you sell locally only, avoiding shipping costs.