First off,
Welcome Fayces!
End Users are the Holy Grail of domain sales,
The treasure at the end of the rainbow,
The ultimate people you would like to find, to purchase your domain.
They are the actual "Users" of the domain.
Not flippers, brokers, etc...but the actual people who have a solid plan for that particular domain,
who will actually develop the domain like we all would like to do...
End Users are all around us...
The question of where to find them is a matter of persistence.
It is a highly covered subject here, with many different approaches, and methods.
1 example, say you own the domain GoCart.whatever
Search Go Cart in your browser, and you will get the first 10 links of websites which use that specific term.
Most likely someone trying to sell GoCarts, or service them will be interested in buying that exact term.
Just read your but off, and you will learn tons from this forum.
Oh, also use the search link,
enter your term, and it will provide you a wealth of info on whatever you may have a question about!
Take Care!