I don't think City spend their time driving up the transfer fees for players like Pogba, Sanchez and Fred, to make them even more rich than they already are with the signing on fee.
If that's the case it didn't work out to well with VD at Liverpool.
Sanchez and Fred chose Utd over City simple as that whether it was due to more money doesn't really matter they chose Utd.
I think if City were deliberately driving up transfer fees most clubs would have got wise to it by now. City aren't the only club out there who doesn't like to be messed about.
This conspiracy theory about City driving up transfer fees for Utd is synonymous with the well worn "we didn't want him anyway."