2007 Ford Fusion Engine Knocking from oil change?

So I’m looking at buying this car off of this guy and the engine knocks. He says the engine knocking is possibly from desperately needing an oil change, and that his mechanic cleared everything, that’s just what super needs to happen to get the knocking to stop. He messaged this morning saying the knocking had gotten much worse after not driving for a few days, he did take another thousand off his asking price though, and it’s down to 1000 bucks (cars are very expensive where I live that price is unheard of but labor and parts are also very expensive)

I know nothing about cars, did the oil settle while it sat? Is it still just the oil? Is there something bigger wrong? Should I risk paying taking it to my own mechanic before buying it to have it looked at? If it’s shit then I’m out that money, but if I buy the car then I’m out the price of the car and left with a car with a broken engine on my hands.

Any help or advice is greatly appreciated, signed a girl who knows nothing about cars and has no money to buy one but needs one for work.