Chelsea used to get away with it for years - seemed particularly good at fetching big transfer fees from China, and I remember Klopp managing to get way over the odds for some of the deadwood he inherited like Benteke, Sakho and Ibe.
It's about being in the right place at the right time though. Someone like Lo Celso might fetch a good fee given his relationship with Emery and his explots for Argentina, but it'll be a small handful of clubs who might also have other options. Whereas I can't see anyone paying for Winks or Ndombele even though they've probably been better players for us overall.
It's also the image a club has, Liverpool got big fees for some of these players because Klopp made them all look good. When we were flying under Poch we cashed in on a few players (nowhere near enough).
I think the value for top 6 clubs in selling players is getting some good youth players, identifying that they aren't good enough for your first team quickly and being prepared to sell them at 21-22
Man City got good money for Lavia and Bazunu. I remember Liverpool got good money for Ibe, Rhian Brewster, Grujic, Hoever etc.
I mean Skipp might be one of our top sellable assets right now, maybe some fans won't want to hear it but if Spurs don't think hes good enough they should probably look to sell him now. We missed our chance when cashing in with Dier, Alli, Rose and Winks and we are a worse squad because of it.
Teams won't want to buy players if they are no good, we might actually have to sell someone who is quite good to get some money in and clear the squad.