For 20M? Are you sure? Not to mention we had the players for cover/trade - Isla, Padoin.
Just through Licht's short injury we've seen how crippling relying on Isla / Padoin as starters in that RWB position is to the team. There's not a ton of players who can provide what Licht has provided for us in his position and even fewer who would be low risk at the price we'd have to pay for them(remember, we paid 9 m for half of Isla). If PSG were really interested enough in him to give us 20 m, we'd definitely have to consider it, but we'd also
need to have a suitable replacement lined up, which is easier said than done.
Giach and especially Matri were good sales. But both were mostly luck, rather than a part of a master plan. Giach, at least in my eyes, looks more like the player we should build up just so we can cash in on, but when you look at the details -the deal ain't impressive at all.
Well opportunism is a big part of the Great Man's transfer policy and any type of sale like the one you're suggesting is inherently opportunistic. We're not really a selling club like Porto, Benfica, Ajax etc., so building up players for big money transfers isn't really a part of our plan, nor that of most other big clubs. The biggest current club I can think of that's been a "seller" is Dortmund, and in many cases they've not been doing it willingly, but via buyout clauses or expired contracts. Even in the cases where they did sell willingly, they had replacements lined up which filled the gap well. In cases where we can do the same, we should and usually do.
Marchisio for 35M to Monaco? Quag for 10-15m a season ago? Giovinco....
The problem with such valuations is that they're mostly rumours. If we could have gotten 15 mil for Quags, then personally I think we'd have done well to sell. A big problem we have will selling Marchisio, however, is that he's one of our only good homegrown players, so filling the gap he'd leave in the squad would be difficult. He's not a PDC type player who's slot you can fill with a rock and not notice the difference. Giovinco was just a horrible mistake.