Bob declared his car to be worth $18k in 2023. Fred fills in an official form, pays $18k to bob, and takes bobs car. Perhaps a 1 month handover period is given, and perhaps a 10% 'hostile sale' fee is given to the government to prevent abuse of the system to take houses from grannies.

Lets say any item worth over $10k (including cars, land, houses, companies, etc) would be part of the system.

Another way of looking at it is "all items in the nation are always for sale, and if you don't want to sell you better choose a high price".

Obviously if you don't want your stuff taken, declare a high value. But you'll pay a bit more tax for the privilege.