If you sell an item for $10 and the buyer pays with Paypal you will have a net payment of $9.46 in your Paypal account.

Ebay will charge you 79c at the end of the month, if you have your account set up for automatic payments from your Paypal account then that is where the payment will come from leaving you with $8.68 more than you would have had if you had not sold it.

(all amounts are approx and worked out very quickly in my non mathmatically inclined head lol).

They are different payments to different companies for different services.