eBay secretly over charged sellers

I sell a lot of smartphones cloths and electronics that’s  why I can’t post here Audiogon 
after speaking with another  eBay representative he told me this : the buyer is going to pay tax on my item so whatever tax applies then they’re going to charge me 12.55% of total amount 
For me this means they’re misleading us with 12.55% they’re lying 
why do you have to charge me the money I did not receive? So if the buyer is going to pay $20-$40 more for tax why do you have to charge me as a seller on that money (tax)  I’m not going to receive? Doesn’t really make sense 
If so then we all sellers are paying separate TAX  before fees so the BUYERS 
when you go the details of the transaction all this tax BS is not there only shows fees 

@dill 
my bad the customer was unable to explain to me 

Before PayPal and eBay got separated I never pay more than 3% on PayPal  or 10% eBay so I don’t know 🤷‍♀️ where 3.5% PayPal fees  you’re talking about 

@dill the item I sold was local pick up so shipping does not apply 
technically what they’re doing is add the tax amount to the final sale price so they can charge you more that’s scam 
so my case they’re charging me 12.55% base on $583 instead of $550 I sold it
what a scammers