Like just about all manufacturers try to avoid the air suspension. It's not necessarily more prone to failure it's just that they all cost big money WHEN things go wrong. So you either budget accordingly or roll the dice...
Pano roof never caused me grief but I must have only opened it a handful of times during my ownership. Again, check for seals/dampness in the cabin.
Standard headlights (non-xenon/LED) are shocking. I remember seeing many that had some really poor quality aftermarket options fitted. So if you see those avoid as they could cause grief on the circuits/error messages.
A friend had the burmester sound system on his and the amp went. It's a super rare option as it cost £3/4k when new. So when he tried to get it repaired he spent ages looking for someone that knew how to repair.
Another failure prone item - wheels. Or rather after market/cheap copies. Avoid. Stick to OEM only.
Connected to the wheels - a few folk I know reported suspension components failing. I reckon it was the over sized / wrong wheels/tyre setup they ran.
The only scary item that I read about when I had mines was where the transfercase failed. Some folk got lucky and had Porsche to pick up the bill but others were left with a few K to spend.
Unfortunately depending on the age of the car you may find many that have been abused, run on a shoestring, poor parts used, or shall we say owned by wrong 'uns.