seeing some of the undesirables you get on public transport, I can sympathise with guards wanting to hide. Would you go and tackle a party of half a dozen youths clearly under the influence?
We do it all the time - it's the job. 90% of the time you can have someone get on stinking of drugs or drink and they'll have a ticket or pay up, slightly grudgingly or otherwise.
Prejudge the people and the problem and all you end up doing is scaring yourself - I actually had a colleague have a near breakdown towards the end of their training because they got so worked up about being on a certain route on their own having paid too much attention to mess room horror stories.
Occasionally you'll get some grief and that's part of the job and it's down to your wits and personality to manage that.
99% of being a successful member of customer facing railway staff, whether it's a guard, RPO, OBS, dispatcher etc is knowing how to talk to people and behave.
Never talk down to people, address them in a similar way to how they address you (unless they're obviously angry) and remember that most things can sail freely overly your head. Talk to every single person who shows you a ticket, even if it's just a quick thumbs up, grin and a cheers pal. If you're nice to other people you'll be amazed who will help if you get into difficulty.