(1).How does one know when they have a bad ball joint & (2). Is it best to buy from nappa verses OEM because they give lifetime warranty. Cause if I buy from nappa they will keep giving me free replacements since the ball joints go bad all the time

 

Ball joints usually start creaking and clunking before they go bad but a bad joint doesn't always make noise. You can also check for play in the joint by jacking up the car and compressing it with a pair of pliers. As far as NAPA parts go for it. I don't have any experience with them but the ball joints are usually good for 50-100k