Usually there is no "the owner". I don't know which deals are supposed to be suspect, but e.g. Akanji was pretty cheap relative to performance. The biggest shareholder owns 8 % of the club, while 2/3rds of the shares are free float. That's a huge amount of people to bribe, or alternatively you have to bribe the people closest to transfer dealings while simultaneously hoping that no one questions the fact that they're damaging the club.
Alvarez was considered pretty cheap, although he hasn't had the best year so I'm not sure how true that is anymore. River Plate is owned by fans/members, so that's no go. Once again you would have to corrupt some sort of transfer team, though I don't know how they decide, without raising suspicions.
Bernando Silva, perhaps? €50m-70m, depending on who you believe. Monaco is owned 1/3 by the House of Grimaldi, which would be a challenge. 2/3 by Dmitry Rybolovlev. Most doable so far, but still.
All this is also just looking at buyer/seller in isolation. It would also be extremely important that no other club would be willing to pay a transfer fee equal to or bigger than the official fee, because if that happened everyone would instantly notice that something is wrong.