Tamara Wilson considers herself an equal-opportunity flirt. She banters playfully and purposefully with her butcher (who sharpens her knives at no extra charge), with security officials at the airport (one let her onto a flight even though she'd left her ID at home) and her female UPS driver (who now leaves the packages on the porch).

"I've used my big, blue eyes and smile to get everything I ever wanted," says Ms. Wilson, 52 and the owner of a Seattle marketing firm. "Flirting opens doors."

Flirting can cause problems, too. Ms. Wilson was no longer invited to a colleague's exclusive Christmas party after she engaged in some racy repartee with a married male guest. And she says she may have lost clients because they misunderstood her "verbal volleyball."

Is it still OK to flirt? Many of us like to flirt on occasion with friends, co-workers or passing acquaintances. When you are in a committed relationship, though, flirting is more complicated. What constitutes acceptable flirting depends not only on your intentions, but also on how your significant other feels about it. (Hint: If you are keeping it secret, you are probably flirting with disaster.)

How can you tell if a person is flirting, or just being friendly? It isn't easy. The uncertainty is what makes it exciting.