Recently, I've taken to being more upfront with passengers about where I draw the line/what I think is acceptable. Of course your mileage may vary but it seems to work for me.
Accepted a fare in Rose Bay about 10pm on Saturday night. As I got the the passengers I could see they were both drunk,a nd what looked like father & son. The son sat in the passenger seat and I explained that they both looked quite intoxicated and I was reticent to accept taking them anywhere. The son immediately explained that he hasn't been drinking at which point I gave him a look of incredulity. He then just as quickly folded and said yep, fair enough. Glad I did as he was even more drunk than he first appeared. His old man was still making his way into the back seat of the car at this stage when his son called out that he had to get out. His dad was confused, and I had to explain to him that he's too drunk, i'm not into taking any risks and he had to leave. He wasn't happy. In fact he let loose a few choice words but I actually found it funny and eventually he could see that there was no discussion.
I cancelled the fare and noted "safety concern". Within 5 seconds I got another fare request just around the corner. Much better outcome.
Later than night I got a fare from Oxford Street. 4 young pax pile in. One with Macca's (food and drink). I didn't start the meter and stated that I don't allow any food or drink in my car. They professed they wouldn't eat or spill any. I stood firm, explaining that I've had too many accidents in the past (it's a lie ... haven't had any) and immediately they opened the door and threw out their food and drink. On the street !!!
Interestingly on the way to their destination we got chatting, they turned out to be pretty cool (and pretty drunk) but I could sense they had respect for my decision. Even commenting they would do the same inf they were in my shoes (with regards using your own car). They left me a 5 star rating ( I saw their update and also their comment with specific mention of things we chatted about).
In any case, just wanted to share. Much depends on the pax or situation. I don't have hard fast rules but I do think in some cases I'll enforce "my rules" from the outset in certain situations (like above). I have a high rating and can afford a few 1* ratings. I think it's my best tactic ... If I think things won't end well, I'll call it up front. If they argue ... i'm prepared to end the trip right there.
Which reminds me I need to change a rating for a pax that farted in my car !!! That's just rude