Teardowns I've Worked On
Answer to "Why is my laptop alternating between a grey screen and normal display?"It is possible that the display cable that connects the screen to the motherboard is damaged. You could possibly repair it yourself, but if you have only had the laptop for two days, then return it to the store and get a replacement one!
Answer to "I spilt coke on my MacBook Pro with touch bar, but it's working fine"I would shut down the MacBook and wait until you are certain that everything has dried out (at least a couple days). Then if everything appears to still be working you could continue to use it. If, however issues do develop, then I'm afraid that taking it to the Apple Store would be your only option as the 2015 MacBook Pro is not very reparable and furthermore, replacement parts are not readily available. Hopefully though, everything will just stay working. Good luck!