how many beers will you serve?

what is the limit?? like i work the dayshift, & regulars come in & sit & drink beer all day. it makes me nervous once i hit six… today i served a guy nine bottles of beer, he was there for hours & he usually drinks a lot when he’s there, & he wasn’t driving… he wasn’t visibly intoxicated, but idk it just makes me feel so nervous😭😭 i don’t like serving people that many drinks. the bartender at my work served a guy 15 DOUBLES, plus like 5 beers, so idk???? is there a number you’ll cut people off at, regardless of circumstance?????