Signature gatherers have to be of voting age and residents of the state. They wear badges saying "I'm a volunteer" or "I'm paid to collect signatures." They are expected to witness the signatures they gather-- and they get a short training in a webinar or Youtube video....
In some states, maybe—but not in Massachusetts, where there are no requirements at all for signature gatherers, and only brief instructions on page 17-18 of the Secretary of the Commonwealth's State Ballot Question Petitions. And those instructions focus on what counts as an "extraneous marking" that invalidates all the signatures on that page; see Question 7.
Question 9 of the LWVMA's Study of the Ballot Question Process in Massachusetts asks: "Should there be regulations governing signature collectors?" Question 10 asks "Should the Secretary of the Commonwealth provide training opportunities for signature collectors?"
Questions 9 and 10 are on pages 11 and 12 of the Study Guide.