Ah, you have made a common error here with the way Steem works. The Steem is not in the till for 7 days.
Downvotes do not take Steem that is owned, they redirect Steem that has been earmarked. Up until payout time when the Steem moves into an actual wallet, that Steem is still in the pool and is open to negotiation. For seven days the Steem is in the stake-directed market flow and not until it is in an account wallet does it become owned. Once owned, it is owned and it is up to the owner what they do with it.
No one is taking money from a shopkeepers till.