Just installed new screen on iPhone 5s, getting weird ghosting/burn effect
There's not much you can do aside from having the screen replaced again, maybe checking the connectors on the inside. 

What I'd do is just buy a new screen online, but make sure that I get a good one. Usually, the old you-get-what-you-pay-for applies to iPhone parts, so my advice would be to spend a little extra and get a nice digitizer assembly (screen) and be sure to buy it from a US, UK, Canadian, or Australian seller. Usually, I buy them for around $50.

When you get the new screen, have your friend put it on and have him return the faulty one for a refund.