When exchanging Iphone do they open it up?

Alright long story short I bought an Iphone off Ebay and the DO NOT REMOVE sticker is gone and I am having issues with the screen flickering green and black like it is not a good connection, and I was wondering if I was to take it to a Apple repair store do they normally open up the iphone before exchanging it or do they just look at the water sensor on the headphone jack?

They normally open it up before exchanging it. You gambled, you lost.