Factoring, or invoice financing, is very common in business. There's at least one poster on here who does that for a living. The difference is that Barcelona owe the financing company money, rather than Liverpool.
It kind of happened when Shinawatra took us over. John Wardle & David Makin had put loans of £22m into City at that point. Shinawatra offered them cash for those, but it was quite a bit less than £22m. They took that cash and assigned the total £22m to Shinawatra, so that the club now owed him the £22m. Which the little rascal took back in full when ADUG bought us.
But there's a better story about transfer invoice financing. When we bought Sergio in 2011, it was something like one third down and two further instalments. Atletico factored the two future instalments to get the cash but the FA wouldn't sanction the transfer unless they knew how Atletico had done that and where they got the money from. Atletico said that it had come from an investment fund in an offshore tax haven (think it was the BVI) but there was a stand off as the FA wanted ot know exactly who'd provided it.
They agreed to tell, provided it wasn't made public, whoch was accepted. However, the provider was described as a NW businessman who'd made his fortune from selling the chain of high street betting shops that bore his name. Now I took that to be Fred Done, the well known United fan, as I can't think of anyone else who fits that description.
If that's the case, the Agueroooooo moment was courtesy of a wealthy red.