What's the best way to try on shoes in shops? Do I need to do something extra when I get home to ensure I've made the right decision? Or am I just being *too* picky?

I think I must be doing something wrong. I have been trying for about a year to buy comfortable, casual shoes for everyday wear. I'd like some ballet flats or sandals in particular.

I try on the shoes in the store, starting with whatever seems closest to my size and going up or down from there. I walk around in them for a bit in the store, and try to avoid busy times when I won't be able to focus because there's too many people around.

When I find some that seem to fit well, I buy them. The next day I plan an outfit around the new shoes, wear them feeling very cute, then within an hour or so I've got blisters and red marks all over my feet. Or find that they're too small (I never seem to end up with any too large).

Is there something more I should be doing to test them in store? Or should I be breaking them in somehow? I'm feeling very stupid and frustrated. How come I can figure out exactly what's wrong when I'm at home (within minutes, usually) but can't manage it before I make the purchase?

Lately I haven't bought any new shoes even though I need them, just because I don't trust my own opinion anymore. I've labelled this as an Ask Angie, but I'd love to hear from anyone who reckons they've got a good system.