If someone buys you a drink

the problem is, the thankyou may seem like progress when it's the opposite

I'll thank them and chat, but I don't feel obligated to them.

If a person asks to buy me a drink and I have the opportunity to refuse, then I would say I would owe them the courtesy of talking with them if I accept.

On the other hand, if the drink just appears and the bartender points out who bought it, I don't think I owe them anything. In a bar, a "free" drink is usually an attempt to manipulate someone. (Not necessarily sexually. I have had windbags buy me drinks just so they can keep me there and keep talking and talking to me! lol)

No one is obligated to do anything just because someone bought them a drink or even any other gift.

A thank you will do, or you could even politely say thank you for the offer, but no thanks.

I have always been the one buying and it has always ended up in conversation. But if they want more than that, I am good to walk away

If a woman buys you a drink, it means you're "in like Flint." 😎

No. You are not obligated. Just signal or say thank you.

Not necessarily but at least thank him for the drink

if they bride, no

If a random person was to buy me a drink I'd politely decline in case it was spiked/drugged in some way.

Like you I am not a bar person and have never been to bars/clubs/pubs with the express aim of finding women to 'pick up' for ons/nsa sexual encounters.