KNOWING MORE THAN YOU'RE TELLING

Eleven years ago, at a neighborhood yard sale in Somerville, Mass., my soon-to-be son-in-law paid 25 cents for a 1930s-era electric fan made by Diehl. The woman who sold it to him was unloading some clutter from her very cluttered home. He got it home, cleaned it up, fixed the motor and held onto it until four years later, when he decided to unclutter his own home.

After doing some research online, he discovered that people were paying more than $100 for similar fans, so he decided to list his on eBay. He ended up selling the fan for $150.

My son-in-law says that he had no idea what the fan was worth when he bought it -- he simply liked its looks. But his experience begs the question: If he had known how much it was worth, would he have had any obligation to tell the seller?

Precisely that question came up a few weeks ago, when P.J., a reader from Timonium, Md., e-mailed me about what he refers to as "unknowing little old ladies who have yard sales." When they have their sales, he writes, professionals show up as early as possible to spot the valuable stuff, which they buy at bargain-basement prices without ever letting on what they know.

"They may pay $10 for a $10,000 vase," P.J. says. "That makes it a profitable transaction for the crafty, but what about the little old lady?"

For his part, P.J. writes, if he goes to a bank to change $20 and he's handed $50, he knows that he has an ethical responsibility to return the extra money. So far as he can tell, the two situations are essentially the same.

"If I know that a vase is worth five figures," he says, "don't I have some obligation to inform the owner? Would it make a difference if the owner is a pauper and I'm wealthy?"

My take on this is clear-cut. At a yard sale, the rules are simple: The seller tries to get as much as she can for an item, and the buyer tries to pay as little as possible. If the seller wants to know if any of her items are particularly valuable, she should take the time to do the research before the yard sale, the way my son-in-law did before listing his fan on eBay. The buyer has no obligation to inform the seller that an item may be worth more than she is asking, even if it's worth far more. And that holds regardless of how wealthy or how poor either the owner or the buyer may be.

But P.J. goes a step further: What if the owner directly asks the prospective buyer how much he thinks the vase is worth, he asks, and the buyer says, "Five bucks, but I'll give you ten"?

"Surely," P.J. writes, "it's not ethical to lie."

He's right, of course: It's not ethical to lie. But there's a difference between lying and not divulging everything we know, and often telling all isn't in our best interest. To volunteer your bottom-line best offer isn't a good negotiating tactic, whether you're working out a corporate merger or haggling over a yard-sale find, and it's not unethical to negotiate cannily -- again, if you can do so without lying. Rushworth Kidder, the executive director of the Institute for Global Ethics in Camden, Maine, once told me about a woman who said that she found that she never had to lie, because she had so big a vocabulary.

If the seller asks how much the buyer thinks an item may be worth, in short, he's wrong to lie to her -- but not obliged to answer her at all. The right thing for him to do would be to respond by telling her how much he's willing to pay for the vase, ignoring the question of its value or his opinion on same. He's not there to appraise her goods, he's there to get a good deal. That's how yard sales work.

Now, if P.J. would e-mail me the address of this neighborhood where $10,000 vases are going for 10 bucks, I'd be obliged.