Money laundering could look like this (I am not for one minute implying that this sale is part of that your honour) ...
Some people have a LOT of cash that they can not account for and can certainly not bank it. This is becoming a pressing problem for those with a lot of old £20 notes 'in stock' as they need to be spent or banked before being taken out of circulation . The date has not been announced , but when it is you have 6 months to bank them or spend them. So starting to get rid of them now is the wise thing to do for certain people. Twenty pound notes are favoured over £50 notes at this level as they attract less scrutiny when using in day to day spending.
One of them finds an 'asset' with a fancy name lying in a field and buys it cash from the farmer, this asset is put up for sale in plain sight , the advert states many legit types of payments including 'cash on collection'
Someone, possibly in cahoots with the seller buys the asset - which, on paper looks like a luxury item - collects it (not) and hands over the cash.
The seller then banks the cash (cleans it) , and if questioned can (sort of) show a bill of sale for a luxury item , the money is then shared between the parties involved.
It might be a bit far fetched and a convoluted way of cleaning a bit of cash but it's a method that is used by some. Not this seller, I might add officer...
It's done all the time with art, property, cars, watches, boats etc etc etc. Private criminal gangs all the way up to corrupt govt officials are running these scams all the time to layer and eventually clean up money,