I bought our stroller from a Facebook selling group for my area. For reference, it is an Uppababy ("the" stroller around my area). The current model retails for like $800 and the second chair for another kid for an extra $150.
I paid $250 for all of it.
It is two models ago (2013) and apparently the new seat configurations are better for two children if one is bigger, but since I only have one kid now and we would like two close together I did not think it was worth spending so much more for a new one. From what I can tell, once the new model comes out, for nice strollers like Uppababy, you can expect about that return -- I saw others trying to sell their used ones for $400ish and they were lowering prices since there is a glut of them, always. They are good quality and they last, but the flip side is EVERYONE tries to sell theirs, lowering the price you can command.
Also, I have not seen people get a lot of offers trying to sell clothes. Probably best to sell as a "lot" on ebay or donate those.