Hi, @emyount.
For Meetings and Webinars, any registrant sharing their personalized registration credentials does indeed open up the possibility that any recipient of this information can join your session. I always mention in emails to attendees that the registration link is your personal link, not to be shared with others.
Requiring authentication helps, in that often times, the recipient will simply click the link and then, when met with the requirement to log in, abandons the effort to join. A knowledgeable or persistent recipient will continue and login, gaining access to the meeting and impersonate the original registrant! Meaning that their Display Name will be whatever name was given by the original registrant.
I’m aware that some testing has been done which shows that requiring registration and authentication does not enforce a restriction that only the person to whom the registration has been issued can enter the meeting. It only requires that the Attendee be logged into Zoom with any account, even if it does not match the account of the registration. Most hosts wrongly assume that registration + authentication ensures that only the Registrant can enter.
Note that Zoom Events (and the single-session variant called Zoom Sessions) can enforce a match between the login account and the registration account. For each ticket type in Zoom Events, you can specify “authentication by Zoom login” or “authentication by email”, the latter being an option which specifically allows someone to enter without being logged in – but they have to enter a 6-digit code sent to the email address used during registration to ensure they’re actually authorized. If you’re interested in this additional level of security, let me know and I can discuss the pros and cons of Zoom Events with you.
I highly recommend not purchasing a Zoom Events or Sessions license until you've had a conversation with an experienced Zoom Events customer and have a good understanding yourself of how Zoom Events licensing works, otherwise you can make a costly mistake which is extremely difficult to undo.