It wouldn't surprise me if, in the future, we start to see a trend where buying clubs like Man U start to disguise themselves when trying to buy players. A good illustration of this is when they signed Martial - the selling company had previously agreed to sell him to Spurs not long before, for about £18m. When Utd came knocking, the selling club knew that United could afford a lot more than Spurs so in the same scenario charged double what they had been happy to receive from Spurs. Yes, in an open market where United weren't under pressure to sign, then that may not have happened but I guess that if Spurs had gone back in, rather than United, the fee would have been much closer to the original £18m.
Therefore you can see a scenario whereby clubs will work through agents to agree the fee without giving away their identity in the negotiation, thus masking their potential buying power and preventing the selling club from pumping up the buy-price accordingly. Whether agents could be trusted to keep the secrecy of their buying club clients is another matter entirely...