Quick question: how do Bangkok blowjob bar bar-fines actually work?

Came back to the hotel half-drunk and still thinking about the bar fine dance been to Nana, Soi Cowboy and a few smaller joints tonight. Usually you sit, buy a drink for the girl (they'll insist), chat, then if u want to take her out bartender mentions a bar fine; pay that, pay her lady drink(s), and there's the separate 台面 deal when you go for short/long or full service it's two different bills and don't let anyone mix them up or claim extra later.

Tip: tell the girl before you leave what you expect (短鐘 or 長鐘, or just a walk and no more), get the bar fine confirmed by the bar staff, and keep cash separate so you can walk if the exit turns into a bait-and-switch; avoid shouting or grabbing, just pay the agreed fees and move on if it smells like a scam. 全套服務, 日按, 泰國浴 talk happens later if both agree tonight was decent, not bad, but I'm tired so gonna sleep...