Q: What do you do when a guest responds to an RSVP with a plus one and you didn't invite a plus one?

A: It depends on the type of event and the identity of the plus one.

If it's a seated dinner or reception where there is limited space and a seating assignment, you can say, "I'm so sorry, but this is a more structured event, and there is no room for plus ones." But if it's a cocktail or dinner party, you should be able to fit in one more person.

Also weigh how important that plus one is to the guest and to you. If it's a small gathering and your invited guest is bringing a random friend you don't know, it is definitely OK to say no because the additional person is not meaningful to your life. On the other hand, if the extra person is the guest's longtime partner or an out-of-town family member, keep in mind that saying no also might cause the guest to decline.

MARC SIEVERS, entertaining expert and cookbook author

A: If you have flexibility on head count and want to avoid an uncomfortable situation, just let it go and make accommodations for the uninvited extra.

Yes, your guest should have realized a plus one wasn't an option, but not everyone pays close attention to an invitation. They often note the day, time and location and ignore everything else (such as instructions on preferred attire). Although you might have an urge to give the guest a call and deliver a lecture on etiquette, you'll be able to better preserve your relationship by letting it go.

If you don't have any flexibility to add people, let your guest know. Be sure your tone isn't defensive — delivery is everything. Politely say, "Unfortunately, your desire to bring a guest can't be accommodated this time, but I am looking forward to seeing you at the event."

TORI TAIT, entertaining expert at ThoughtfullySimple.com