There are many downsides too, for instance foreign clubs are afraid to buy for having to negotiate with two clubs with conflicting views and valuations to buy a players. eg: Juve couldn't sell Sorensen because Bologna didn't give consent, now his valuation/price probably gone down.
Mitigating risk most often means lower returns, fingers in too many pies. eg: Immobile 1st half for Boakye's 1st half, seems only Immobile 2nd half will earn the money some of it will be lost on the loss on Boakye, we literally got no money for Immobile's 1st half (I guessing half of Boakye won't get us much).
Also sometimes some clubs has to make compromises to keep a good rapport with the other club, eg. if Juve wants stake in Cuadrado then Juve will prolly have to deal Isla as Udinese wants it done. this for me is the reason blind auction cannot and wouldn't work for too long.