How to tell that a latch really is a good one
A typical conversation in my life:
Parent: I know the latch is good but it still hurts.
Me: How do you know the latch is good?
Parent: I saw (insert doctor, public health nurse, other support person) and they said it was fine.
Stop right there.
If your latch hurts, it's not a good latch.
I promise. If it hurts, something is wrong.
A good latch is one that is effective and pain free
In order to know that you have a good latch, you need to know that it doesn't hurt and you need to know how tell that your baby is drinking. Identifying drinks takes practice, and sometimes its hard to do with new babies who are drinking colostrum, but if you watch, you can see the baby get a big mouthful of milk and swallow it. Usually, after the first little bit, baby starts to pause with their mouth in a more open position. That's a big mouthful of milk. They swallow then do it again.
Watch those drinks. Watch them slow down and then add compressions to get them going again. This will help baby get as much milk as they want and keep them drinking, which will help keep you pain free.
Some other things you can try to help get a pain free latch -
Line your baby up so their nose is in line with your nipple so that when they latch their chin in into the breast and away from their chest. Try to keep their nose away from the breast as well to help achieve the optimal 'asymmetric latch'.
Pain when breastfeeding can happen for lots of reasons, but generally, a well latched baby who is drinking, isn't going to cause pain. Someone who is helping you with breastfeeding should be able to tell you that the baby is drinking well and you can tell them if it hurts or not. Together you can determine if it's a 'good latch' or not.