Correct, 1099 added to your total income which goes through differing bracket %s as you tier up... there's a gaming level up joke in there somewhere
You don't just pay top side % across all. Most people on this forum would likely fall between 22 and 34% tax rate on top side income, incrementally scaling through the differing tiers as income increases.
You wouldn't get a 1099 issued at 500 bucks though, just once you cross 600 threshold. Those paying entities are then required to issue one. So in your example, that's $60.6K:
$0 to $41,775 taxed at 12%
$41,776 to $80.1K taxed at 22%
Those #s changed if married & filing jointly.
So I'd personally view it as 600 bucks inbound, zero taxes paid thus far on it, zero pre-tax deductibles against it (401K, medical, etc) so 22% bracket of $600 = $132 owed to Uncle Sam when filing income taxes off $600 paypal sales
Basically any 1099s I get each year, I save 1/3 of it, planned for my taxes. Usually just lowers my refund but like to be safe.