I would not buy a car online. If I happened to see a car listed online (unlikely, because I don't look... but let's say I did) and it was local to me, I might decide to visit the dealership and see it for myself, and test-drive it, etc., but surely I'd have visited the dealership ANYWAY if it were close enough to me and I were looking for a car?
I would not buy electrical goods from an online seller. (I exclude b&m shops that have websites; I mean I wouldn't buy a computer, a sound system, an iPod, a phone, etc. from someone who only has an online shop, or is a Chinese seller on eBay or Oztion etc., or is an Australian seller on eBay or Oztion selling on goods obtained direct from ... yes, you guessed it, China. The risk of fakes is, in my opinion, too high, and the sellers often don't offer anything LIKE the after-sales service of a b&m shop.)
I don't buy clothes online. I like to try them on. I need to see if they'll look fantastic ON ME, and I need to look at the stitching and workmanship closely.
I don't buy shoes online. I need to walk in them to be sure they'll look great and feel comfortable.
Some sorts of jewellery I wouldn't buy online - if it's important that I check the colour and clarity of the stone, or see whether it suits my skin.
What about you? What won't you buy online...?