Seeling has been since the dawn of time. Already in Championship Manager 02-03. I believe it's made so the game is a bit harder (sort of an artificial difficulty).
It's always tricky because when you want to sell, you know you can't put the guy on the transfer list, because he loses a lot of value and clubs will offer close to nothing. But if nobody bids, you're stuck.
And also, something I find extremely annoying in that FM: AI clubs almost always ask in their offer for the selling club to pay some of the wage. That's not realistic either. I'd be curious to know if that's already been done IRL. Yet AI refuse to make offers without that.