Alot of people don't understand rabbits & don't bother finding out more, they just give up & confine the rabbit. It may be a good idea to start by being sympathetic to the problems they are having & then give them some help e.g. neutering, hand feeding etc. That way they will consider you a helpful, friendly person and will be more likely to take your advice.
I do find it tempting to wade in & tell the person not to be so stupid - but the consequence of that is people stop listening rather quickly!