Bellew, 33, won the belt by beating Congolese Ilunga Makabu at Goodison Park in May in what he described as the "biggest fight of my life".
He takes on Flores, 37, at Liverpool's Echo Arena after the American hassled him for a fight on social media.
"Everything he has said he's going to pay for it," Bellew told BBC Sport.
"I understand if people are asking if I am struggling to get up for this. But when I step between the ropes I fight for one thing, and that is my life. And I can't back down.
"His mouth has got him this fight," added the Liverpudlian. "He's been following me for two years saying I'm not a proper cruiserweight, I'm a bum and he'll knock me out. But it doesn't mean anything until you get in the ring with me. He's writing cheques he can't cash."
Flores is a former American national amateur champion and has won 32 of his 35 professional fights, with his most recent defeat coming against Kazakh Beibut Shumenov for the WBA interim version of the world title.
"It has been a dream of mine my entire life to win a world title," said Flores. "So many people give up on their dreams and say 'I can't do this, I'm not good enough'."
Flores has also sparred with a handful of elite-level fighters in his hometown of Las Vegas, including British heavyweight David Haye and WBC light-heavyweight champion, Canada's Adonis Stevenson.
"I don't care who he's worked with or sparred because it's different with 10-ounce gloves," added Bellew, who has 17 knockouts in 30 fights.
"He's a good fighter, yeah, but is he world title level? No. Not a chance. His last fight wasn't even for a proper world title. Every big fight he's had he has lost."
Britain's Tony Bellew says he needs no extra motivation for his fight with BJ Flores on Saturday when he defends his WBC cruiserweight world title.