The Tosun deal looks like it 100% is going to happen. Normally I would say its typical Everton, and its going to fall apart, but there are some massive differences between this and the Mata hype for example.
Tosun said goodbye to his fans. Then he flew to London and has been milling about on vacation, clearly not about to go back to Besiktas, not in Liverpool to avoid impropriety but close enough to get there quickly. He has made up his mind, hes going to have his move.
The president of Besiktas didnt come to Liverpool on a whim, he did so to close a deal, and one he was sure was going to be closed, whether or not he could squeeze out a couple million more out of it. Both Tosun and Besiktas overplayed their hand, its purely a matter of when but my guess is he signs tomorrow and gets a late announcement. Previous deals that fell apart didnt have a player practially already move to Liverpool, and didnt have a teams president actually fly in after that fact to finalize a deal.