I don't think anybody paid for the food at Quarks. They paid for drinks, service and so on. Although Quark did refer to having crates of Yamok sauce sitting around unused.
The drinks served at Quarks were mostly real, although how he managed this given that his customers were from all over the galaxy. Can you imagine a bar offering to serve every different beer on Earth ?
When Worf had his Bachelor party he made everyone Fast and go through trials lol anyways when the wedding was supposedly off O'brien and Bashir then took the oppourtunity to order food from Quarks and just as they sat down to eat it Sisko takes it away and says that the wedding is on, if i remember correctly Quark says to Obrien and Bashir that they are still paying for it.