Where can you really be 100% sure of your Fortnite Acc. To sell?

Don't even want to read that it's forbidden. I can't do anything with the Acc and I understand the consequences.

However, it is some value and a try does no harm, so on which page is it offered or could it also work on Ebay?

EBay could work.

In any case, be careful not to scam it! This is often done