To think when people send this type of text ...

[MarigoldEntwin]

“Not sure if I can make it but I’ll let you know”

It means 9/10 times they’re cancelling and have no intention of going.

Or they are waiting to see if something better turns up .... either way it is very rude.

Sometimes it just means what they say and there are factors they don’t want to get into that will impact their answer.

I think it’s also used when people who aren’t very assertive gets asked to do something by someone who generally doesn’t take no for an answer and will probe inside out any decline of an an invitation from them.

Yep. They're not going.