If you sell by direct mail and are acquiring new mailing lists, make sure that the names you're getting aren't ones you already have. "It's gotten to be a very incestuous world out there," says Gordon Segal, whose company, Crate & Barrel, has been mailing out catalogs for about 10 years. In the early days, he says, he didn't worry much about duplication between lists. "The overlap between lists you had and lists you bought was maybe 10% to 15%." Lately, however, the dupe rate has risen to more than 30%. "Everyone is looking at the same people," says Segal.

So before you shell out money for new names and addresses, you'd be wise to test the lits for overlaps. Otherwise, you may get less than you pay for.