I used to work for a catalog and online sportswear company and I have taken a few things to heart:
1) It is worth every penny to go to a specialty store. A *good* specialty store. One that will sell you what you need, not one that tries to sell you a popular brand/style just cause.
2) Most serious runners whether competiting or not find the right shoe manufacturer for them and stick to it. We were told if the customer's history only ever showed, say, Saucony, don't suggest a different brand if the Sauconys were out in her size.
3) This is no time to be stubborn about shoe sizes. Nikes are -or were notorious for being 1/2 size small and running narrow, tor example. So if you find Nike to fit you best don't have a "no! I'm always size 8!!!!" moment when the sales clerk fits you in an 8 1/2. I used to hear store clerks (certain stores could order through us) having battles and the too vain female screeching about how she ALWAYS wore a 6 and she wasn't going to order a 6 1/2.