The usual story, it wouldn't turn on. The first place I start with GBAs, in particular, is the power switch. If it's dirty it can prevent the device from starting or it can affect the "quality" of power, i.e. the power LED flashes from green to red.
Although the board itself looked in good condition, once I lifted the whole thing out, it turned out a transformer (better known as T1) had cracked open and the coil of wires were all over the place. I replaced that and power returned.
The original GBA had a funny story attached, it was in an original pink shell and the (I assume) kid that owned it wanted something "cooler" (again, assume, but indulge me), so they used a black marker pen all over it.
However, this board was destined for the teal(ish) shell and available to buy.