It was hit on the pass side rear quarter panel, so I did look there to see if I could see anything inside the wheel well, nothing looked too crazy but I did notice a section where they put it on, so I know the quarter panel was cut and then replaced with another part.

 

You could have had just the QP's sheet metal damaged to the point where it's easier to reskin it vs banging it back out. The frame (or better described as unibody) could have been left undamaged.

 

I used to run a body shop and we repaired a few totals and then sold them. When the repair bill is 70-80% of the value of the car an insurance company will total the car. So, your car had major damage. Where the car was repaired will make the difference. If the body shop had a good frame machine and measuring sytem, then the repairs could be good. If the body shop was a dump, and many are that do salvage title repairs, then you don't know the quality of the work. Start with the paint, is the finish smooth and does the color match? Most body shops that repair salvage title wrecks will use cheap clear coat which will fade in a year or two and may flake. Since you stated the damage was a side impact, look at the gaps all around your doors and the body. Are the gaps consistent and are the doors flush with the body. I would be certain the door sills were replace, so look at the spot welds around the door openings on the body and look at the welds underneath in the door openings. If the welds were not quality you may hear squeaks when the body is stressed from hard turns or bumpy roads. Salvage titles repairs are hit and miss and most insurance companies will not offer comp and collision for this reason. Good luck.

 

Another issue with salvage cars is unseen wiring damage. In an accident wiring gets Pinched or cut. Sometimes the harness is replaced, sometimes it's not seen. Over time water can get in, oxidize and corrode wires and 1-2 years down the road you have issues

I would never buy accident salvage cars. They are just never the same. Sometimes they have alignment issues, creaks etc.

It's why salvage cars are cheap. Of course, now that g35s are so cheap, they can be salvaged for minor issues like interior damage or vandalism.