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Online versus in-store. Convenience is a major advantage—the Internet is always open! Whether you're hunting for a particular item or just browsing, even after looking at six stores you'd never get the overview you do online (and think of the gas you save...). Often it's cheaper, too: A site is forced to be competitive because shoppers can instantly compare prices. 

The good-fit challenge. Pre-shop at stores and see what size you are in a given brand. You can also use customer service: "'s team has tried on the clothes and knows whether they run large or small; they live and breathe the fashion," Phair says. 

The extra-cost trap. Always check a site's returns policy, taxes, shipping rates—it shouldn't be coy about this info. If additional charges aren't factored in, the lowest price listed online may not be the best deal. 

Timeless versus trendy. Clothes from past collections won't look dated if you choose classics—like a nice, clean blazer, not one with statement shoulders. "These days designers produce things that can carry for a number of seasons," Phair says.

Number-one navigating strategy. Filter your searches by size—"It eliminates options that you shouldn't even be looking at!"

Real or fake? Authenticity is an issue, especially in the "pre-owned" world, Phair says. Her rule of thumb is that if a sale seems too good to be true, it probably is: If someone claims to be selling a brand-new off-the-runway item for more than 80 percent off, it's almost certainly a quick copy.

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