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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."

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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.