Where to buy replacement screens?

Hi,

Last year I started fixing iPhones for my friends to make a few extra bucks (I'm a high schooler, so I can't get a full time job).

For the new screens on 4, 4s, and 5 I have just bought parts on ebay. I had one or two fail, but in general they almost all worked fine. Now I have started to do 5s repairs. I have gone through three screens I've gotten on ebay( two from same seller and i tried a 2nd seller), and they have all failed. It appears to be in the LCD connector, as many worked before they were bent to fit in the frame. Am I doing something wrong here? I've never had a 5 issue, and the process is almost exactly the same. And if not, where do any of you who own repair shops buy your parts? I know ifixit sells their own, but by the time I charge for my labor and the part it ends up being cheaper to go straight to apple. What reputable site could I buy parts from, or do any of you know a specific ebay seller that has quality parts at a reasonable price?

Thanks so much

Nick