If you sell a thing on eBay does eBay get half the profit
It depends on how you sell it, what you list it for, what it is, and who you are. Paypal gets you for about 2.9% + .30cents. Listing prices are sometimes free. Usually 10 to 50 cents. eBay charges a final value fee and more for fancy listings.
may not be 50% profit but as an agent for the seller perhaps 20%
6% fee when I used it