You are right ofcourse but I do think it has to be within reason.
Outright refusing offers of above 100m for a player you only paid 15m for youself. I mean obvioulsy they can make a profit and obviously they can try to get as much out of it as possible but honestly the way these clubs are acting (it is the same with Liverpool) it feels like they are keeping their players as prisoners. Ok they signed a long time contract but my god how hard is it for those players to get a transfer to a better club if the opportunity presents itself. If the player doesn't want to stay, than I think as a club you need to sell, as a club you only should want players who want to be at the club, if they really want to leave you should let them. If Dortmund would have accepted something like 100m for Demebele, I'am sure they would be well compensated and I'am also sure that there wouldn't have been this much hostility between the player and the club as there is now. I mean you can conclude business in a normal sensible way without blowing up bridges and souring relationships, fighting it all out in the press but that requires all parties to act sensible and be reasonable. I don't think Barca and Demebele are out of order for asking for a transfer and offering Dortmund a big amount of money to do it. Dortmund asking money as if Dembele is the best player in the world, imo that is unreasonable.
Again they are asking for x10 their investment. 2nd highest transfer fee ever paid for a player, 50m more than Pogba cost us which was seen as an insane amount only last year. I don't know but I find it over the top. They can surely do this but imo it is really being unreasonable.