(MONEY Magazine) – Next time you want to check out a new travel agent, use this simple test. Tell the agent that you and your spouse need a vacation. Someplace warm and relaxing but with night life. Ballpark of $3,000.

If the agent suggests a Carnival Cruise Lines excursion, then you could be a pigeon for one of the longer-running promotions in the travel industry. Since 1981, the line has dispatched its field force into randomly selected travel agencies, posing as customers and giving a story like the one above. If the agent recommends a cruise, the salesman hands him $10. If he recommends a Carnival cruise, he gets $1,000 cash on the spot. Carnival defends this gambit, which has given away more than half a million dollars since its inception, as a way of building business and finding out what travel agents are recommending. Says senior vice president Bob Dickinson, who crafted the program: ''The chances of misfiring are slim. In eight years, we've never gotten a letter saying, 'Hey, my travel agent misled me.' '' ! Not everyone is so enthusiastic. ''I think it's a deceptive practice,'' says Ed Perkins, editor of Consumer Reports Travel Letter (301 Junipero Serra Blvd., Suite 200, San Francisco, Calif. 94127; 800-999-7959; $37 a year). ''People ought to know whether a travel agent can be taken as an unbiased counselor or an announced dealer of particular products.'' Certainly Carnival, the leading cruise line, is not the lone offender. Competitors have offered such prizes as fur coats or cruises to agents who achieved a certain quota. ''I've heard of worse ways to sell a product,'' shrugs Jerry Mitchell, chairman of the American Society of Travel Agents' cruise industry committee. Still, if an agent pushes a cruise, press him about activities and entertainment, cuisine, cabin size and ports of call. Find out whether he has sailed on that ship. Talk to other clients who have. And if you have any lurking suspicion that you're just the travel agent's ticket to a fur coat or a free trip, ask about that too. ''If agents have any financial incentive for pushing one package over another, the cards should be on the table,'' says Perkins.