I was fortunate to have a two-night stay in Rome last month. On my first full day, I had tickets for the Vatican Museums in the afternoon but no morning plans. So I decided to take the subway to the Colosseum stop and see what that scenario looked like.

Tourists were lined up everywhere, zig-zagging across the grounds. And it seemed like everyone had a selfie stick. (One of my favorite signs later in my trip was a picture of a selfie stick at a museum entrance with a big X through it.) It was not quite the Roman holiday I had envisioned, when a young man came up to me with—it would soon be made clear—lots of marketing wisdom.

"Do you want to join our tour?" he asked. "We have just four spots left."

Here's how he got me to sign on (with some supporting notes from the field):

Instant access. He knew that I could see the chaotic line situation and promised that his group—my group—would go in immediately. There would be no wait. I would feel special.

I probably stay with my cable TV distributor for one reason—when something goes wrong and I call them, help is immediate.

Entrance into a new community. He told me that his group of eight was just over there. "Come join our group! [You're by yourself. Groups are fun.]" And then, sensing my interest but skepticism, he took me over to them. He was right—the people were real and looked fun. I wanted to be a part of this community, talk to people who had the same mission I did.

In their most recent report on keys to excelling digitally, The New York Times encourages creating more communities. "We know from research and anecdotes that readers value the limited opportunities we provide to engage in discussion [with others]."

Strong leadership. He introduced me to the guide. She had all kinds of identification and plaudits around her neck. She reiterated that we would go right in and laid out some quick history of the Colosseum—starting with a few short stories. I was joining a well-run group with a knowledge-steeped guide.

A founder of Twitter, Biz Stone, said: "I realize that half the job of being a good leader is making sure everyone knows everything at all times that they need to know, because it's human nature to fear the unknown. And in the business world, fear translates to the assumption that something's going wrong... So I try to over-communicate."

Reasonable pricing. The cost was 27 euros (around $30). I think entrance alone would have cost around 15 euros, and that line was quite long. It's hard to ever put a price on our time, but on a vacation it's certainly quite high. Actually, with as many hats that we all wear at work, time is always at a premium. 27 euros did not sound like a lot.

Don't underprice. "You have to believe that your product is the best, and the pricing is right," said Liz Slovenkay, membership director for insideARM.

The offer will expire very soon. When Mr. Italian wiz marketer first encountered me, he said that there were just four spots left. When he brought me over to the group, there were just two spots left. And sure enough, the guide looked ready to roll. I needed to decide quickly. Once again, the fear of missing out was stronger than any savings I could get.

"The fear of potentially 'missing out' on information [or a global landmark] is an excellent trigger to get people interested in your content [or tour]," Belle Beth Cooper wrote a couple years ago. People respond more to the negative. The words "no," "without" and "stop" did better than "do" or "start" in subject lines.

No one in the group had a selfie stick.

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Ronn Levine began his career as a reporter for The Washington Post and has won numerous writing and publications awards since. Most recently, he spent 12 years at the Newspaper Association of America covering a variety of topics before joining SIPA in 2009 and SIIA in 2013 as editorial director…