Unsure about Used Car

I am looking into buying a used car from a small time dealer and I am
suspicious it might have some maintenance issues. Hoping someone can help
me understand a few things:

1. The car was on when we arrived. They didnt start it in front of us, not sure if
that is suspicious at all, any reason why they would do that?

2. There was a long red wire exposed to the left of the steering wheel and next
to the door, thought it was odd since you don't normally see that. I asked the
guy why it was there and he said he didnt know. Any ideas on why that was
there? is that normal?

3. The dashboard had a yellow light on while we test drove it. It was a yellow
triangle with an exclamation point inside. I asked them what it meant and they
said it was probably an oil change needed or it wasn't reset. Seems odd they
wouldnt just pay the $20 for an oil change to get that to go away. Anyone
know what that light means?

Overall i'm getting some red flags from this car, its just $600 below KBB price
so not cheap, how can I put my concerns to rest?