Second hand is great if you know what you’re doing.
It’s a fluid market and so those with the most knowledge should be able to use this to get the best value.
I picked up an unused GR Agressor XCR from a guy on Ebay who’d claimed he’d ridden it loads, but it was just to make himself look good. The chain had zero wear, the halfords sticks hard no marks, and it had the bobbles still on the tyres. Easy to see on ebay pictures. £300 for £1000 of new bike (included decent pedals and computer).
Also part of the skill is to spot the dog that’s been oversold as new and shiny… Unless the price is great!
Other times I’ve been unsuccesful because my competition have the same information to make a purchasing decision at the price I want or above.