One of the benefits of buying lunch from an expensive food market is that the stallholders are obliged to be polite and make conversation. This is not something that you encounter regularly, if at all, as a Londoner. 

These interactions are a good opportunity to push the realms of acceptable conversation; a chance to test dialogue before using it on people that matter.

Here's a recent example (to the best of my recollection):

Me: Enjoying the rain?

Pastry seller: It's terrible, the rain keeps everyone away.

Me: I'll have a brownie please.

Pastry seller: I much prefer it when it's sunny.

Me: I don't think London was ever meant to be sunny.

Pastry seller: [Silence]

Me: Well, thanks for this, bye!

From this I can either surmise that my statement about a suitable climate for the capital was so profound that there was no response worthy of my perceptiveness, or that it was simply such an odd and obtuse thing to say that she didn't know what to say.

I'm leaning towards the latter.