What are some items that we should never buy preloved for kids? What about breastpumps?

I read an interesting blog post about pre loved breast pumps and it basically says that whether or not giving away a used breast pump depends on what type of pump you have, whether it's an opened or closed system and ultimately, personal preference. http://mythnomore.blogspot.se/2011/08/why-you-shouldnt-buy-sell-or-borrow.html?m=1