If I buy a widget for $100,000 and sell it of for $105,000 do you expect me to pay income taxes on the $105k or on just my $5k profit? The former would be absu

If I buy a widget for $100,000 and sell it of for $105,000 do you expect me to pay income taxes on the $105k or on just my $5k profit? The former would be absurd and in most cases would make it impossible to be in business-- you'd take a net loss on every transaction unless your markup was greater than your tax rate. Good that went through fewer hands would be astronomically less expensive. So why do you think that it's weird that a landlord doesn't pay taxes on the portion of his income that goes to the costs of operating the business?