I can’t sell my A level/GCSE books

I’ve listed my all my A level and GCSE books as well as other novels on Gumtree (50+) but nobody’s even asked about them, let alone buying them.

They’re all at half price or much less but it’s still not working.

I’m wondering if I should use eBay, but aren’t there 2 taxes you have to pay on top of delivery and postage costs?