eBay collects and remits sales tax from buyers in all US states that require it. FVF is calculated on item + shipping, not on tax.
Important: sales tax collected by eBay does NOT increase your FVF. Tax is handled separately.
Average US sales tax: ~7.3%. Buyers pay this on top of your listed price.
No. eBay charges FVF on item + shipping only. Sales tax is collected from the buyer and remitted separately.