Chali 2na Sean Thornton has done a pretty good job of explaining the treatment of transfer fees from an accounting perspective but maybe this will help?
All businesses have practices (amortisation or depreciation) to spread the cost of an asset (in this case, Rhodes' registration) over the UEL (useful economic life - basically how long you expect to use it for). In this case, that's the length of Rhodes' contract: say 4 years.
30/6/17 Year 0: Wednesday's balance sheet has a £10m asset on it - the P&L (where FFP is focussed) shows zero
30/6/18 Year 1: Rhodes is valued at £7.5m. The £2.5m difference is charged to the P&L as amortisation.
30/6/19 Year 2: Rhodes' balance sheet value is now £5m. Another £2.5m is charged to the P&L.
and so on.
It changes if the player signs a new contract or is sold: this roughly what happened with Jamie Murphy for us. The fee was undisclosed at the time but lets say it was £290k. Murphy's contract was 3.5 years (coincidentally 29 months)
30/1/13 Year 0: new asset recognised on balance sheet £290k
30/6/13 Year 0: five months after he signed, Murphy valued at £240k, £50k on the P&L
30/6/14 Year 1: Murphy valued at £120k
30/1/15 Year 2: Murphy valued at £50k but signs a 2 year contract extension. This changes the amortisation from £10k a month to £2k a month (as the UEL is extended from 5 months to 29 months)
30/6/15 Year 3: Murphy valued at £40k
30/8/15 Year 4: Murphy valued at £36k (two months into 15/16) but is sold to Brighton for £1.8m. The P&L would show £4k of amortisation then a "profit on disposal of asset" of £1.764m.
Clear as mud, eh?
Not quite: you can only recognise the difference between a player's book value and the selling price. If Wednesday sold Rhodes in two years' time for £5m they'd not make any profit. If they sold him for £3m they'd have to take another £2m hit.