Generally when selling something you don’t want to talk about the negatives of it however for something like a car or TV which generally is an expensive purchase, mention some small problem, scratch, defect that they weren’t going to notice on their own and that doesn’t really jeopardise the sale.
Then when you go on to talk about how everything else is in full working order etc, they will conclude your your unnecessary honesty that you’re a honest person and everything else is as you say it is. They then won’t lowball you, unless they’ve been on here reading up on it 😉
You can also use this technique on an online auction website or for sale website