In real life, things like this don't happen because in a store, an items price is clearly displayed for the consumer too see.
On Meepcraft, you have to do /find to see the price, and most people don't want that inconvenience or don't know how.
When you buy something, it should say somehing like:
"The price of that purchase will be (number) meebles. Are you sure you want to buy this?"
You would type "yes" if the price is reasonable, but "no" if it tells you it will cost 120k for 3 wool.
This would really help prevent Vshop scammers.
Also, staff should have the power to remove ridiculously overpriced items from Vshop.