The suspicious posts began appearing on Craigslist on Thursday afternoon, a few hours after health officials in Massachusetts announced a key expansion of who could receive the coronavirus vaccine. “Companions” to those older than 75 were now eligible, the state said, but only if these caregivers helped accompany seniors to vaccination sites.

Suddenly, it seemed on the classifieds website, plenty of younger residents wanted to start spending time with septuagenarians. Especially if money was involved.

“Some people [are] posting online, trying to get a senior to bring them to a vaccination site, or in some cases asking to be paid to drive somebody to one,” Massachusetts Gov. Charlie Baker (R) said at a news conference Thursday, calling the ads “pretty disturbing.”

The ensuing fracas over the “companion system” has since been criticized by some state lawmakers, who say it all but guaranteed to encourage dangerous scams and failed to ensure that Massachusetts’s most vulnerable populations receive the vaccine first.

“We shouldn’t be having people haggle for vaccine appointments on Craigslist, Facebook, and other social media sites,” state Rep. Tami Gouveia (D), a public-health social worker, wrote on Twitter. “This isn’t safe, equitable, or effective.”

As larger and increasingly diverse pockets of the U.S. population suddenly find themselves able to sign up for a vaccine shot, the episode may preview the difficulties associated with prioritizing broader, more nebulously defined groups.

When the shot arrived in many parts of the country, hospitals and nursing homes took on the responsibility of distributing it to their essential employees. Seniors who began to qualify in ensuing weeks could prove they were eligible simply by showing the age on their IDs.

But granting strict priority to essential workers such as day laborers or farmhands, whose job arrangements are often more informal, as well as groups defined by a personal practice such as smoking, may prove easier said than done. There is no clear answer on how — or whether — officials might corroborate that an individual is in those groups and meets the threshold for a vaccine.

In Massachusetts, the companion system was conceived as an attempt to solve an existing problem in the state’s vaccine rollout. Like in many other parts of the country, technologically challenged seniors had struggled to navigate a complex website of appointments and frustrating scenes at vaccination sites.

On Wednesday, state officials said that caretakers could start signing up for companion appointments on the same day as the seniors they were transporting to a vaccination site. It was the state’s first exception made for residents who fall out of Phases 1 and 2 of the state’s immunization plan.

But by the time of his early afternoon news conference the next day, Baker and several Democratic lawmakers had taken note of potential schemes on Craigslist.

One person in Boston reportedly wrote that they “Will PAY $200 to assist 75+ year old with COVID vaccine process,” according to a screenshot by state Rep. Mike Connolly (D).

A Cambridge resident said they were “Paying $100 to book with eligible senior for vaccine.” And in Brookline, one ad made an offer for “Free Pickup and Dropoff for Covid Vaccine.” (All three ads appear to have been taken down as of early Friday, although similar offers remain online.)

Many Democratic state lawmakers seized on the posts to criticize Baker for this and other aspects of Massachusetts’s immunization campaign, saying it failed to address the obstacles that had been preventing senior citizens from easily getting shots.

“The companion system will put thousands of healthy adults ahead of those who have the most significant risk of getting and dying from COVID-19,” a group of a dozen Democratic lawmakers, including Gouveia, wrote in a letter to Baker.

The group said the strategy could prove “dangerous” for seniors, “opening up opportunities for individuals with mal-intent” to prey upon older residents who lack reliable transportation or are in need of additional sources of income.

They suggested that Massachusetts should instead adopt a wait-list policy, by which young, healthy adults can sign up for last-minute appointments in case of cancellations or extra doses remaining.

But while the policy is in place, Baker offered a warning to elderly residents at his news conference. He urged them not to share their personal information with strangers and to report any potential scammers to the police.

“You should only reach out to somebody you know or trust to bring as your companion,” he said.