We have learned through years of experience, there are so many chinese knock off parts available that it's impossible for them to give good quality control. Ebay and bulk buying phone repair shops are selling you the cheapest stuff they can get their hands on - and that makes sense in a profit and competing perspective. I look at things from a business perspective however, returning unhappy customers are something nobody wants - the client or the business owners. These parts may be cheap, but you really do get what you pay for. Corrupt graphics, lines on the screen, dark or light spots, erratic "phantom" touching of the display are just a few problems that can occur literally weeks after the screen is installed. There is nothing wrong with the method behind the person who has installed the screen, if there was the issue would be there from day 1. There is an inherent fault within the screens which makes them simply not last, through no fault of anyone other than the manufacturer. We only install screens we get from reliable refurbishers of iPhone screens. This means you get a phone screen alike the original, the LCD and touch parts are exactly the same apart from the glass covering the display. This ensures you are getting genuine Apple quality display and touch responsiveness every time. The difference in cost is minor compared to the cost of the repair (usually £10-15) and provides you with a like for like original other than the glass.
Cheap iPhone screen repair is a failing business model, we always want to do things right and see our customers have a lasting repair.
The above image is an all too common sight on a phone that has recently had it's screen replaced at rock bottom prices. It doesn't necessarily happen straight away, but within a couple of weeks you get issues.