Which is a valid point indeed, although in my case where I wasn't convinced which way it was and it wasn't until the second week it may not have worked. And then remotely convincing someone could be hard opposed to demonstrating it in the shop.I actually prefer to buy on line as your better covered.
While you can try out a lens in the shop you might not encounter any issues until you shoot a certain scene (i had this with Jessops a few years ago). Trying to convince a shop that its a faulty lens when they cant reproduce it can be a pain. Buying on line gives you at least 7 days (a month with Amazon) to try it out while being under no obligation to keep it.