I am sure it won't be long before some politicians decides the govt needs to be the middleman in EVERY transaction (less X% for taxes). It is their money after all.
They would dearly love to do this, for that reason. Private, cash sales represent a significant amount of tax evasion.
Never mind that sales tax was originally paid on the item when it was originally bought from a shop.
And that shop paid taxes on the gains.
And the buyer paid taxes on the income used to buy the item.
And paid taxes on the fuel used to go to the shop
And paid yearly taxes for the vehicle they drove there.
And paid taxes on the building they driving the item back to.
We are taxed to death, and somehow, it's just never enough for the politicians.