Understanding Taxation Through Formalization Via Shares

Slave prices are necessarily estimated absent an actual slave market. Even then, outside extraordinary cases only the slave caste gets bought and sold, so slave prices of peasants, freemen, &c would still need to be estimated, although we would at least know the critical determinants of slave prices. 

However, if you were genuinely doing it properly, each person would be a publicly traded corporation. Simply tot up the market cap of $ALRNS and there you go; that's how much I'm worth. A minor share would carry an obligate dividend, based on your earnings, exactly as with fictive corporations. Perhaps a wage job could be formalized as a significant share. Slavery is merely when someone owns all your shares.

Thus we can easily formalize taxation. When you're born, the State arrogates a certain amount of shares to itself, something on the order of 30%. It return it makes promises to you it may or may not keep. If you make too much money it starts arrogating more of your shares to itself.