Best online source for refurbished laptops

Hey all, I've narrowed down my choices thanks to this sub and relentless searches here. I didn't see many recommended sources.

I'm looking at backmarket, Amazon and eBay. Not sure on any recos on an ebay seller.

Amazon has a 90 day return policy which is great, backmarket is 50/50 on reviews

Trying to stick win an X1 Carbon <$600 USD.

Any input is greatly appreciated