Wife wants to use ebay to sell stuff, how does PayPal work

I sat and did the math a while back because I was doing a lot of selling (little business venture) and needed to know how much I was losing to Ebay & PayPal so I could price things so that I made $$ too - - it might have been 19% - call me a liar for 1%.. 20% is a rough figure that works. Sell an item for $100 and you might realize $80 if you are careful.
I have been selling on Ebay for 12 years , fees are not 20% . The fee is 10% but will be offset by 2% if you ship in one day and abide by a few other rules . Paypal will take another 2.75% but if you set-up with their CC they kick back 1.5% with every purchase . How else are you going to get worldwide advertising ?? The only real ***** I have is they charge you the 10% selling fee on the shipping also ( for the last 2 years, to get rid of the guys charging more then the shipping was worth) .
Feel free to PM me with any ?