I recently asked a niece with a lovely house in rural Maryland if she had ever offered it to friends when she was going to be out of town. Yes, she nodded. “They must have thrown a party,” she said, wincing at the memory. Furniture had been moved around, a treasured bottle of bourbon was now empty, “and then I found a beer can between the sheets.”

Rule #1 for travelers staying in someone else’s home: No beer in bed. And rule #1B, no parties without permission.

“Stay at my house” is a wonderful offer. What could be better than enjoying a friend’s (or friend of a friend’s) home for free? It’s a delightful way to travel. The price is right, and the ease of crashing at a fully equipped place can beat even a sweet hotel room. On the flipside, loaning your beach condo to a pal or, say, her sister as you are off traveling can be a nice way to share the wealth.

But what are the rules to keep these home loans and house swaps from ruining a friendship? Read on.

Rule #1: Don’t Invite the Whole Neighborhood

Remember, this isn’t your home. So no parties without express permission. Indeed, to paraphrase Susan Cornwell, an occasional house-swapper with a place in Washington, DC, no guests—period—without pre-approval by the host.

Even if you disagree with the rules of the person loaning you their home, ahem: It’s their home. When Anne Penketh, who owns apartments in Paris and London, swapped one of her places with a couple in Los Angeles, she thought she’d spelled things out ahead of time, saying, “You can have people for a few nights because there’s a sofa bed, but it doesn’t really sleep three.”

Don’t assume it’s fine to bring friends and family without asking for approval. Yes, even if they aren’t present when you arrive, the homeowners may hear about it.

Nevertheless, they arrived with a grown son who would be staying the whole month with them. “I thought, Sh*t, they should have mentioned that!” she recalls. That’s the kind of experience that can make a person less than eager to share their digs again.

(If you’re thinking there’s no way for a homeowner to find out about extra guests if they aren’t there for your arrival…guess again! Between home video alarm systems and nosy neighbors, word can get out!)

Rule #2: Get It in Writing

We’re not saying you need a legal contract to borrow or loan a house for a weekend. What we are suggesting is that hosts should prepare a tip sheet—and guests should take the time to read it.

Says Susan Cornwell, “It should include house alarm codes, wifi passwords, and how to operate the heating and/or air conditioning. Also, if a person often lends their house for longer stays, how to operate the dishwasher, washer and dryer, how often to water the plants, and when and where to carry out the trash would be helpful.” 

If you’ve said “Stay at my house,” leaving a list of alarm codes and wifi passwords is a wonderful touch.

And, might I add, a list of streaming services and brief remote-control instructions on how to enjoy them would be a nice touch to a “stay at my house” visit. The names and addresses of nearby grocery stores, restaurants and transit stops would be appreciated, too, if time allows.

“All houses or apartments have quirks,” Susan continues, “like, say, how to operate a wonky shower faucet or a jiggly front door lock. And … where are the towels? Is there an ironing board?”

No joke. If your silverware is kept in a drawer with a hidden slide-out, please give a sign, as I found myself thinking that a borrowed house in upstate New York was BYOF (bring your own forks).

With homes in Brooklyn and Barcelona, Gail Robinson and her husband, Bill, have been both lenders and borrowers. “We are constantly editing our sheet of instructions and re-editing it and proofreading it,” Gail says. “It looks like ‘War and Peace.’”

Rule #2B: Try Not to Ask 40,000 Questions

Not everyone leaves a thorough guide to their home, however, which is all well and good. And there can be conundrums even if there are, such how to operate the home’s music system.

In general, it’s best to minimize how often you pepper the loanee of your lodging with questions. It’s likely, if the homeowners said, “Stay at my house,” that they are off traveling or otherwise engaged. So send only the most urgent questions, if possible, vs. a constant stream of “Do you have beach towels?” and “How do I open the beach umbrella?” queries.

Rule #3: Do Unto Others

It may seem obvious, but if you are a guest and you break something, fess up and try to replace it. “Things have been broken and they never told me,” says a rueful Anne Penketh. “You think, come on, guys!” 

If you break something, own up to it. Then replace it or offer to pay for it.

One woman we know, who prefers not to use her name as she still cringes at the experience, recalls taking a friend of a friend up on a kind offer to stay in her West Coast lake cottage. “Unfortunately, I reached for my phone in the middle of the night (thanks, insomnia!) and sent a small glass figurine flying off the nightstand,” she recalls. “I told the homeowner, and it turned out to be a family treasure from her grandmother. I offered to pay for a replacement, and she took me up on it. I left her a $200 check and am now so careful in dark rooms!”

Rule #4: Cleaning Up

Another aspect of this realm: Borrowers and lenders alike are often bedeviled by a related question: Just how much does one need to clean up?

Consensus says at a minimum everything should be clean-swept and in good order. “And I always ask the host before the visit what I should do with the sheets at the end of my stay,” Susan Cornwell says. “Wash and dry them, put them in the washer?” If you don’t get that information, it can be good to take the high road: Wash and dry the linens, and remake the bed, leaving it as you found it.

Also, if you are offering your home up for stays longer than a few days, clearing some closet space and directing your guest to it is a generous move.

Rule #5: Keep an Eye on the Pantry and Fridge

Often, when people offer homes to friends or those who are a degree or two of separation away, they figure their guests will use some sugar in their coffee and so forth. But they likely don’t expect to be cleaned out, as if a bunch of college kids came through the place. Guests should keep track of what they consume and replace it. “I always try to leave at least as much food and drink in the fridge as I found there,” Susan Cornwell says.

Did you run through all the coffee and milk? Don’t leave your host high and dry. Shop around for the same beans and type of milk (even if you don’t like medium roasts or oat “milk.”)

Restock supplies: Don’t even think about leaving the returning homeowner high and dry and without coffee and milk!

And be especially mindful about alcohol. If you finish an almost-empty bottle of whisky, replace it. Hey, it might even be nice to buy a bonus bottle of wine as a thank-you for your host, which brings us to….

Rule #6: Say Thank-You the Right Way

People love presents. Whether you’ve been staying at your best friend’s apartment or her second-cousin’s ski condo, leave a thank-you (no, a text message isn’t good enough). Or leave more than one. Susan Guerrero recalls her way of thanking one friend: “I weeded her front path. Gave her a book from the free pile at the library. Took in the mail. Left her a mini bottle of Moet because she’s the only drinker in her family.”

Weeding may be saintly, but in general, you just need to gauge how big a favor a homeowner has done for you. A single bottle of wine might cut it for a night or two, but if you’ve been enjoying a great place in a coveted location for a week or more, you may want to go grander. One woman we know gifted her host a gorgeous vase from a local museum.

The longer you stay, the nicer the thank-you gift should be, perhaps more than just a bottle of wine.

Here’s one clever tactic: Susan Schulman and her husband, Larry, were getting ready to leave a very nice house in Maine that had been offered to them by friends who were traveling. They made an educated guess and headed to the local wine store, dropped their hosts’ names, and asked for recommendations. “We were able to put together six of their favorite bottles,” Susan says. That’s a genius example of how to show your gratitude for a freebie stay someplace wonderful.