I think it is often a class/age thing too. I recall walking into a store with an executive computer case and I was never hassled but my younger colleague who always used a backpack was routinely asked to leave it (with a computer inside) at the front desk. I would never leave any backpack with anyone without a receipt. I really hate the double standard of them not trusting you at the same time as you are expected to trust them with your possessions with no assurances at all.

It reminds me of my local Tim Hortons where the clerks pass every single bank note they get through a counterfeit money detector. The last time I was there for coffee I got five dollars bills back in change and I checked them through their counterfeit detector personally to make sure I wasn't getting passed any bad notes. That's fine you don't trust me, but what's good for the goose is good for the gander.