For former colleagues I'm personally always willing to answer a reasonable number of questions for free. But after leaving one particularly-unpleasant situation, I did barter that I'd give a friend a brain dump if we could do it over dinner and he'd expense it =*).

This was a freebie since I was sympathetic: supply chain issues hit them really hard.

The employer before that, it was $200/hour and they were happy to pay it.