Big dent on frame: How did this damage happen? I just bought this second hand Ridgeback Impulse folding bike for my partner. I'm a wheelchair user and it was dark and rainy when I collected the bike. 

So... I didn't check it (facepalm) I just got the seller to put it in the boot for me. 

It's been in the boot for 3 days, folded, and as far as I am aware, nothing has happened to it while it's been there. 

Took it to the bike shop (and nothing happened on the way there either), and we notice a big old dent on the frame, in a bad place, which means the bike is unsafe. 

Seller thinks I did it, I think she just didn't notice it. She has no photos on the affected side. It's pretty hard to spot unless you're in the lighting conditions that we were in when those photos were taken. It also looks almost like it's meant to be there - until you realise there's no reason, there's also a crease down the middle of it. 

My question for you guys is... in your experience - how would a dent like this happen? Could it happen from a folded bike in the back seat going over a road hump? etc? What force would be needed to make a dent like this? It's pretty big - and would have been inside the fold if it happened in the car. Just don't see how it could have happened, while the bike was folded, in a car. But at the same time, if it has been me, I don't want to screw over the seller either. 

Help!!

Thank you
It seems that this dent belongs in the bike.

Here is a photo of a similar bike. While image is of low quality, the dent is visible:



However, as pointed out by Lamar Latrell in comments, in your second photo the weld to the headtube has a dark spot in it. I cannot tell from the photo, but you or your bike mechanic should check if it is a damage in the weld seam, or just damaged paint.