This is what is being called the Internet Sales Tax.
It is actually the state sales tax charged by some 34+ states. More will follow since they have been missing the revenue they need for schools, roads, etc.
You don't collect it.
EBay (a US company) is collecting it and taking the easy way out by putting it on your customer's invoice.
The money does not go to you. It does not come from you.
It is a passthrough.
BUT
You will see several angry threads both here and on dotCOM pointing out that Paypal (which is NOT a part of eBay any more) charges its fees on the entire customer payment.
Including those taxes you never touch.
So what you are being charged is 3.4% of the sales tax of whatever state your customer is in.
Long time eBay seller (and chartered accountant) @pierrelebel
has pointed out that retailers who take credit cards are also charged by the cc company on the whole payement they process including the sales taxes. He believes the charge is legal.
Whether it should be paid by eBay is a different question. Most sellers think it those PP fees should be deducted from our eBay fees before we are charged each month.
