A seller never keeps the headline price. They keep what survives the structure and the tax.
Once a catalogue is valued and diligenced, the negotiation turns to how the deal is done, and that decision can be worth more to the seller than another turn on the .
There are two basic shapes. In an asset (or trade) sale, the seller's company sells the rights themselves (the copyrights and the income) and keeps the shell. In a share sale, the seller sells the company that owns the rights; the buyer takes the entity, the catalogue inside it, and everything else attached to it.
To the buyer these are very different risk profiles. To the seller they are very different after-tax outcomes. The same £3m headline can leave the seller with materially more or less cash depending on which route is taken and how the proceeds are taxed.
So the adviser's job is not just "what is it worth?" It is "what do you actually walk away with?", and that is a structure-and-tax question, framed for the client in pounds they keep, not percentages.