For those of us, and I'm one of them, who are thinking about whether or not to get a manager, SAG-AFTRA now has a list of managers who have signed a "Code of Ethics & Conduct" agreement.
Since there are no rules for personal managers - unlike the rules that an agent has to follow - this is a great way to find managers who you can trust (or at least trust more than the ones who haven't signed the agreement).
If you are in SAG-AFTRA, you don't have to sign with a manager who has signed the agreement, but it does offer some protections that you don't get with your average manager.
To see the Code, and other info about manages, follow the link below to go to the SAG-AFTRA website's Manager section. (Anyone can visit the site, even if you're not in the union.) Besides the Code, they have "Do's and Don't," "FAQs," and a list of managers who have signed the agreement.
There is good info on here about what to look for (or lookout for) when thinking about signing with a manager. See the menu on the left side of the page.
SAG-AFTRA Personal manages section