Also, a general precaution. Never plug or unplug the LCD ribbon cable while the DMG is powered on. Doing so at any slight angle might kill the function of the  left and B buttons, because those are next to -19 V drive voltage for the LCD. Always worth pointing out.

Could be a power issue. What he describes as lines on the screen sometimes, could be power that dies after a split second. Might for example be related to the power regulator board in the lower left corner, for example bad capacitors. It could be due to dirty/loose contacts on the power switch, corrosion in the DC jack. (It has an internal switch that disconnects the battery when a DC jack is inserted, and that internal switch could be broken.) But hard to tell without further information. Likely to be fixable, but you need to find the problem.

Would help to see a video of the issue once you receive it, as well as pictures of the internals.

I have literally thousands of components, Including caps regulators, ECT. I salvage electronic components for a hobby with a desoldering iron. So if its a power issue, hopefully, It should be an easy fix. Worst case scenario, its the typical unifixable horizontal lines. But based on the description, It most likely isn't. Which is good.

Would help to see a video of the issue once you receive it, as well as pictures of the internals.

"powers up but nothing shows up on the screen except a few lines sometimes"

After winning I sent a message to get a little more clarification on the issue.

He responded "Hello and thank you for your business. If I remember correctly the lines are horizontal and that was with a game in it. The sound was there but nothing but a few lines on screen. I will ship out in the morning. Thank you."

This seems like the reverse on what normally happens on Gameboys. Usually there is a image with missing lines, Not a blank screen with lines. I wan't to be prepared to repair this and have my Soldering iron, Deoxit, Alcohol, And Qtip, And multimeter Ready!!

Has anyone heard of an issue similar to this? It makes me think its not a screen issue/ribbon issue as this would still show an image of some sort. The unit is in very good condition and I don't think it has ever been opened.

Based on the items he is selling, He is definitely not someone who knows how to repair electronics. So I doubt he did an attempted repair on it.

here are 2 images from the post I purchased it from.