Near the Galt-Marian Lawrence Library off Caroline Avenue dozens of families make their way behind a wired fence toward lively music and an array of tents. The Galt Flea Market, at 610 Chabolla Ave.

Design pros share their favorite flea market treasures—and the common pitfalls to avoid while hunting for secondhand gems.

Thrift stores are generally full of low-value donations, making them best for basics. Flea markets are hubs for those who value an item’s history. Display-worthy decor and clothes are easiest to find ...