I think any club needs two things to be in that position to tell others to piss off: Money (lots of it) and prestige (which comes with results, trophies etc.). PSG is slowly but surely getting there. BVB on the other hand is quite far off, for example.
What I am trying to say is, ultimately it is up to the individual players. As much as the clubs can say piss off, if the player wants to leave, he will find ways to leave. But if the player feels happy because he is being paid and treated really well and he feels his club is prestigious and competitive enough (in the case of PSG), he will stay.
Never said otherwise.
For example, too many people talk about PSG as if they just were a bunch of mercenaries, but Verratti never refers to them as teammates, but as buddies/friends.
That's what he said last week: "I want to continue playing here with my friends."
So of course it plays a role in him wanting to stay.
But let's face it, if PSG was still the poor club it was before, even if they managed to still recruit Verratti at the time (which would not have happened anyways because Juve was also on him), PSG would never has been able to keep him here, whatever if paris pleases him or not.
Being a rich club plays an important role. Prestige will come later I hope. But nowadays you need money first before reaching prestige.
In the past, PSG didn't even have half the money middle table spanish clubs have today. There was some summer mercatos in which our budget was around 6M euros...