Image: Money © Corbis

What's considered good manners changes as society changes. What doesn't change: the principles behind good manners.

"Manners reflect . . . how society views relationships, what is acceptable and what frustrates people," said Peter Post, a managing director of the Emily Post Institute and a great-grandson of the etiquette maven. "Manners change, principles don't. It's about treating people with consideration, respect and honesty."

For example, today it's acceptable and often preferable for people to pay their own way on a first date, Post said, rather than expecting the man to pay. People now see the advantage of getting to know each other without an uncomfortable sense of obligation. That trumps the old rules, where a man was expected to demonstrate his financial wherewithal by picking up the check.

It's still not OK, however, to ask people how much they earn or how much they paid for something.

"We still think money specifics are private," Post said, despite evolving standards about what's OK to share. "It's overly intrusive to ask those questions of someone."

So what do you do when someone does ask such questions? Or asks you for a loan? Or airs financial details you'd rather keep quiet? Or overdoes it in a gift exchange? The ever-evolving rules of etiquette can make it a challenge to deal with awkward money situations, so I enlisted Post's help in handling some of the ones posted by readers on my Facebook page and in emails:

Liz Weston

Liz Weston

"What do you say to a parent when you've borrowed money from them in the past and paid them back, but they bring it up at the most inappropriate moments? For example: 'Remember when we loaned you that money to pay off your credit card?' In front of a gossipy relative nonetheless. Ugh!!"

"Ugh is right!" Post sympathized. You might feel tempted to retaliate by bringing up her past missteps -- "Hey, Mom, remember when you got drunk at Uncle Bill's wedding?" -- but that wouldn't be good manners.

In the moment, the right course is simply to change the subject. If the person airing your financial dirty laundry persists, you can directly ask them to stop. "Mom, I'd rather talk about something else."

Later, you can let the person know privately -- and politely -- how you felt about her inappropriate share, Post said.

"You can say, 'I have to tell you how uncomfortable that made me,'" Post said. "'That was between us.'"

"(My) teenage son . . . kept asking relatives if he could borrow $5,000 for a new computer! Took a while to put the kibosh on that one! He was very insistent."

Just as parents can embarrass kids in front of relatives, so kids can also embarrass their parents. Post said this mom did the right thing by "putting the kibosh" on the shakedown. But he's concerned that a child this age wouldn't know such behavior is unacceptable.

"Why did he ever think it was appropriate to do that?" Post wondered. "Was there something in his upbringing that made him think that might actually be OK?"

Kids need to learn not to ask relatives or friends for money or loans, Post said. Such requests put the other person in a terrible position. More on that:

"Several years ago while visiting family 500 miles away, a cousin asked me to stop by before leaving to head home. When I did, I was asked for a loan because I am 'the only one in the family with any money.' It took ALL my self-discipline to refrain from saying 'Maybe that's because I never give you any!'"

Post liked both the cleverness of this retort and the fact that she didn't actually say it out loud. Trying to preserve a relationship is more important than scoring a point.

But that doesn't change the essential situation that "it's just not a good idea to lend money to family," Post said. "Things can turn sour so fast and the relationship is ruined."

Click here to become a fan of MSN Money on Facebook

More from Liz Weston:

Liz Weston is the Web's most-read personal-finance writer. She is the author of several books, most recently "The 10 Commandments of Money: Survive and Thrive in the New Economy" (find it on Bing). Weston's award-winning columns appear every Monday and Thursday, exclusively on MSN Money. Join the conversation and send in your financial questions on Liz Weston's Facebook fan page.

Anyone who is likely to be asked for a loan would do well to figure out a blanket response, whether it's "I really can't do that for you" or "I don't loan money to family," he said.

"You've got to come up with some level of preset rationale, a consistent message to everybody," Post said.

And you shouldn't feel bad for saying no. "You're not the one who created the negative situation," he said. "They did, by asking you for money."

"How do you handle a relative who wants to know the cost of everything you buy? Last night we paid for dinner (for) 14, since it was a celebration of our son's birthday. This relative asked right out what the bill cost. I pretend not to hear the question but it's getting annoying. How do I put this person in their place gently but get the point across … 'it's none of their business'!"

Pretending not to hear rude questions is a time-honored way of dealing with nosy people, Post said.

Unfortunately, people insensitive enough to ask may be insensitive enough to persist. In that case, you can offer what Post calls a "nondescript" answer. Something like, "It's a reasonable bill, and I'm glad I could pay for it."

Other well-tested responses include changing the subject or simply saying, "I prefer to keep those details private."

"What do you do when people overshare about their financial life? I met a friend for drinks, and he brought along another friend who had just landed a really great job. I know this because she wouldn't stop talking about it, down to the details of exactly how much she was going to make and what her stock options would be worth."

In the Facebook age, privacy is sometimes seen as old-fashioned. Some people regularly share every boring, sordid or embarrassing detail of their lives.

But oversharing about money can be particularly disconcerting, because it turns what should be a social interaction -- getting to know someone new -- into a potentially competitive game of "how much are you worth?" 

"Maybe they're just excited or clueless -- well, this one is definitely clueless -- but I don't think they're thinking about the other people," Post said. "Getting into the specifics [of how much you earn] makes the conversation about money instead of about you."

Faced with such oversharing, Post would change the subject. A good approach might be to ask the oversharer what her job duties will be, or take the conversation in a totally different direction by asking where she grew up or what she likes to do in her spare time. 

"[What do you do] when someone wants to give you a large gift and you feel it's too much. For instance, my brother-in-law has had a really profitable year this year, and feels that he has to 'make up' for the years that he couldn't really do Christmas. Now he wants to buy us something in the several hundred dollars range."

This brother-in-law thinks he's being generous. He may not be fully aware that he's playing the big shot -- and potentially making others uncomfortable.

A similar situation can develop when a more affluent person constantly wants to pay the way for her friend who is less well-off. A more thoughtful approach might be to engage in activities that both can afford. Healthy adult relationships are based on reciprocity, after all, not handouts.

"I think you can say, 'please do not do that,'" Post said. "'I appreciate the sentiment, but that would make me uncomfortable.' "

Rather than put your brother-in-law on the spot, make this about your feelings, said Post. You can follow up with an assurance that there's no need to "make up" for the past.

"What you can say is, 'I like our relationship the way it is,'" Post said.

Click here to become a fan of MSN Money on Facebook

More from Liz Weston:

Liz Weston is the Web's most-read personal-finance writer. She is the author of several books, most recently "The 10 Commandments of Money: Survive and Thrive in the New Economy" (find it on Bing). Weston's award-winning columns appear every Monday and Thursday, exclusively on MSN Money. Join the conversation and send in your financial questions on Liz Weston's Facebook fan page.