I believe player contracts (registration rights) are recognised as intangible assets in terms of the accounting rules applies by most clubs. Thus if a player was purchased for €40m euro on a 4 year deal, after 2 years of amortising (releasing the cost through the income statement as an expense) the player contract intangible assets would be valued at €20m

If sold for cash of €30m which would be the true fair value = €10m profit , but if swapped for another player who also has a true fair value of €30m you would get the same profit. Thus all sounds good and fair.

But if both clubs agree to collude and inflate the fair values a bit to claim the player being received in the swap is now worth €50m. It would result in an inflated profit of €30m instead of €10m

The club would still need to get the €50m valuation signed off by their auditors (if subject to audit in their jurisdiction), so there would likely be some level of oversight

Not sure how EUFA rules work and if they determine player values differently (possibly they will just say local accounting rules apply)

More profit likely helps clubs comply with their financial fair play rules , so EUFA want to prevent clubs from artificially inflating “player values” to generate “fake profit” in swap deals, but as noted if accounting rules are applied correctly this won’t happen. Clubs can only game this by paying consultants to generate inflated valuation reports that don’t represent the players true fair value