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...