People I try to avoid #1

THE BEWILDERED OLD PERSON

This might sound cruel, but you can't imagine the dread that comes with a pleasant, but confused old person. This is the kind of person who toddles into your shop, around mid-morning, and asks you for something you simply dont sell. Something you never sell, and is nothing like anything you sell.
Of course you smile back, and apologise, but you don't sell what they want. This is met with a happy smile, but a complete lack of any other response. Apparently they want more. You ask if there's anything else you can help them with. They ask for the same item again.

This cycle may well repeat itself a few times, but thats alright. They're friendly and polite, which is much more than your average customer, and the conversation appears to be at an end. Or so you'd think.
The dreadful person instead wanders over to another product. He/she really doesn't intend to buy it, but will ask you a great many of questions about it, often more than once as they clearly dont understand a word you say, even though you're describing it in the very simplest way you can think of.
So now we're surely done. They're starting to wander off and you've escaped with only a mild headache. No. They're coming back again. They're asking you for something else that is completely different to anything you sell. They really need it apparently. Again you smile, tell them you don't have it. Maybe you offer a suggestion as to where they can find it. This process will again repeat a few times.
Then they've gone. If you're lucky, that's it.
If you're unlucky, they've simply moved to another part of the store you didn't see. You will encounter them when you least expect it, and will be immediately subjected to another round of either event described above.
This wouldn't be too bad alone. What makes it so painful is that you must never stop being polite and cheerful. To be anything less than kindness itself to this harmless little person would be like kicking a puppy. You can't do it without feeling like a monster.

The only way to avoid this whole situation is to hide when you see them for the very first time. Become busy somewhere else and let some other poor sod deal with it.
And how do you avoid being that other poor sod? Be very, very alert.