The Economist currently has a podcast series about this very topic, it’s called ‘Scam Inc’ hosted by Sue-Lin Wong. They follow a trail of ‘pig butchering’ scammers from their victims back to the scam cities in Myanmar. Very well done and informative.

https://www.economist.com/audio/podcasts/scam-inc

I would usually tip based on the total including free food. So if the total was $20 I would give 15-25% - probably 3 to 5 dollars. In the case of getting just a free drink, I usually tip the price of the drink, similar to what you mention.

As well as some fine, Corinthian leather 🤌