Bad Manners and Brimstone

Refusal to commit is a pet peeve of mine.  I understand people need to check schedules and can't always commit right away - I'm the same.

Absolutely. It’s totally legit to say “I’ll check my diary at home and get back to you” or “I won’t have my next month’s work schedule till Wednesday week - can you wait that long for an answer?”. And there are plenty of people like Mr Rat whose work may at any time make unplanned demands on them, so their acceptance of any invitation is always going to be conditional; and that’s fine so long as that’s made clear to the host.