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Always find here and Pinkbike good for shifting MTBs, where is the go to place for road bikes?
I've sold quite a lot (not all bikes) on Facebook in the last year or two. You can list it in the big 'bikes for sale' groups and local ones. Selling it locally is so much less hassle I only ever use eBay for really niche stuff these days.
Stealth ad in the chat forum could work ?
eBay will get best price (assuming you are sending and not doing collection only) but you need to wait a couple of months as selling in winter is not the best time to sell a road bike.
I'm always staggered by the prices that second-hand bikes go for on Ebay. Just make sure you use one of their promotions such as max £1 selling fees to limit the cut they will take.