@curiousjim Never done your own taxes, eh?
A w-4 is the form you fill out to tell your employer how much income taxes to withhold from your paycheck.
Perhaps you meant w-2. that would be wrong too. a w-2 if for earned income, not sales.
When you sell an asses (such as a stock) you will get a 1099. the law changed requiring paypal to send you a 1099-k if you sell more than $600 worth. If the OP was surprised by this, he must have been living under a rock. Thus most of us don't prefer paypal any more. But it isn't paypal's fault, it is congress.
Now getting a 1099 doesn't mean you pay taxes on your sales. You just have to put it on schedule D. You also enter what you paid for it. Hardly ever do you make a profit on stereo equipment so you'll show a loss. So that's a win right? Now you get to write off your losses on stereo equipment. We all wish. They tax you on profits but you can't write off losses (unless you are a business). So if the OP does get declared a business, he can write off his losses. But paypal does't decide if you are a business or not. They just send you a 1099.
Finally, I am not an accountant. I'm a physicist who does his own taxes and I wrote all this from memory to validate anything this says before using it on your taxes.
Jerry