I think everyone wants brand new stuff for their kids (OK, understandable).
I tried to give away for free, a used stroller, and a used crib mattress. No one responded to my Craigslist ad! I was trying to drop them off at Goodwill in the back, and a clerk ran and out and sternly barked "No, we don't take those!!'
I think it depends on the item as to whether people* want new or used. For example, can it be properly cleaned (plastic great, cloth that can't go in the washing machine is bad)? Was it likely to see a lot of poop or other mess? I can appreciate that certain items people want new (e.g. a mattress), but I've seen a lot other named items described here go fast on my local facebook group, particularly strollers. Just may not have found the right medium for it? For what it's worth, it's illegal to sell a used mattress in my state for hygienic reasons, so I can see that sketching people out, just like people worry about used car seats of unknown provenance. Try yard sales/church sales/online groups in your area/coworkers.
I haven't been posting here because my progress has been so hopscotch around the house, but I am trying to send items out to make up for the kid inflow (have a baby on the way so I can't get rid of the baby stuff). I've regorganized and gone through part of the guest closet with crafting, wrapping paper and other odds and ends. I've gone through half of the dining room cupboard. I've gone through part of the office. I've given away random kitchen items. Conclusion: I really need to pick one area and finish it! My trouble is that I see something and start, but with limited time (^toddler), I only get partway through. And then it's a bit before i can get back to it, and by the time I do I spot another area that bugs me with extraneous stuff that I dive into instead. So when I was wrapping Christmas presents I went through the wrapping paper and then started in on the rest of the stuff in the guest closet. But then a while later when putting away the empty cookie tin for Christmas I spotted some things to get rid of so did that shelf, etc.
*Personally accepted two used mattresses (and 2 cribs & sheets...) from a friend, a used stroller from a neighbor, used infant car seat & associated stroller from a different friend, floor play from yet another friend, many more items from those friends, and bought a used bathtub at a church sale for a few bucks, which I think covers all of the rejected items described above!