Thank you for the responses. I'm thinking of selling baby furniture - things like pushchairs, cot, cot mobile, highchair, Moses basket, walker, changing table, stair gate and bed guard. Please forgive my ignorance, what is an NCT sale?
I've sold lots but yes, 60% is unrealistic unless it's top-end stuff. Bugaboo, Stokke, Boori and Bloom stuff sells well. Cots, high chairs, nursery furniture, buggies. I've had 50% or a bit more for things like that.
Clothes go for peanuts unless they are good brands. And I don't mean Next, which so many people list as "designer" on eBay, I mean Boden, Joules and proper designer clothes. You might get a few quid per item then. Bundles are easier to sell.
What have you got to sell?
With postage, it might be worth looking to do a local nearly-new sale? Rather than NCT sales, I tried a couple of the sales organised by Mum2MumMarket and similar and had a decent amount of success.
I've also heard that car boot sales can be successful for stuff like clothes, but mostly you just get 50p per item for basic Mothercare clothes.
Unrealistic. Unless it is v expensive, lovely or rare, people tend not to want to pay more than about 30% of new price including postage. So something that is £30 new and costs £4 to post, I' d expect to sell for around £6-7. Just my experience. Baby clothes barely sell for anything, even the really good stuff, as there are loads of them.