Does it have lines with every game? If it does than it might be the TV like Frankie says. If it’s only some games that cause the lines I would have to say it’s cheap pins or put together wrong. That’s why if you do take it back take a game that is causing the lines with you.

Also (you probably already did but) you can try cleaning the games more, an NES and a clone are different in where the pins connect at so the pins might be clean where they connect to the clone and not so clean where they connect to the NES.