recapping what's already been posted: The IRS is after income and not imposing a "Sales Tax." So keep note of what you paid for it (like stock transactions) and profit (income). If you sold it for $1000 but paid $1200; that's a $200 loss, no income tax.
As for Sales Tax that may apply depending upon State/Local, but I doubt locals can track online sales yet. In both cases the seller pays Income Tax or Sales Tax if any.
(Not an advisor, just by take) 😉