I think it's really harsh to say it 'sickens' you, LE
Imagine how OP must be feeling
'Like if somebody gives you lovely hand me downs, and your dc wears them/or not - you pass them on. You don't put them on ebay. It's like you pass on that lovely good intention. '
Yes, for sure - I agree with this. but that is different.
The person giving you hand me downs is thinking specifically of you and your child, it is a loving gift, specifically for you. It is done with the intention of you enjoying the gift.
Freecycling some item which you simply don't need any more and cannot be bothered to sell, means putting it out there for whomever wants it/asks for it, it isn't a gift aimed at that person, it is not personal if you see what I mean.
It's done in order to get rid of something.
It's true it might be done in a kind, hopeful-it-will-help-someone-out sort of way, but it is generally to benefit the giver as much as anything - they want it gone.
And even if not, they can specify if they don't want somethihng sold on, if it bothers them that much.
I for one would not object to someone changing their mind about one of my things after they had received the item. You can't always tell what something will be like. I once asked for an old bed and when it arrived it was horrible - the family were pleased it would be used but I hadn't the heart to tell them I wouldn't be using it after all, and in the end it sat outside my house and then went to the tip, it was unsafe. I don't think it would have been appropriate for me to give it back! And truthfully it would have been necessary for me to sell it in order to get rid of it, as the council doesn't take stuff that heavy. Luckily when we moved the landlord took stuff away for us.
OP didn't need her item, but wanted to make use of it - and now she has seen it she has changed her mind.
I think she should be free to sell it on for £30 without compunction.