These are not always easy to get right, but they're worth the time. For example, to solve the first punctuation problem referenced above, you could use something like:
[firstname,fallback=Hey], check out our VIP offer!
If we have a name recorded for our subscriber, Jane, she would see:
Jane, check out our VIP offer!
If there's no name on record, Jane would see:
Hey, check out our VIP offer!