I just make a few assumptions about the world the PCs live in...
1.) The PCs, especially at low levels, are not that unlike other adventuring parties.
2.) Adventuring parties have existed from time immemorial.
3.) Adventuring parties in the past have tended to act like the PCs act.
Conclusions:
1.) The local authorities are "used to" the PCs' tactics and will do exactly the most efficient thing to counter them (esp. sleep spells on low level PCs).
2.) If the PCs are @$$holes, the common people are accustomed to dealing with @$$holes. They assume all adventurers are @$$holes. The PCs don't get the time of day, the barkeep won't serve them, they are automatically guilty until proven innocent, and in general everyone treats them in the manner they so richly deserve.
"Want a longsword? Good. It'll cost you 400 gp. No, it's not masterworked... that gets into the tens of thousands."
"No, I will not cast cure disease on you lawless ruffians."
"We don't serve your kind here."
*little kids throwing stones at the PCs* "Get out of here, we don't want you around. Always making mom cry and beating dad up. Jerks!"
*constant pickpocket attempts*
*deliberately spitting in/poisoning/etc. the PCs' food and drink, knowing that the authorities will turn a blind eye*
Furthermore, the authorities react with extreme prejudice, killing first and asking questions never. If the PCs break even the smallest of laws, they can expect death sentences... preferably at the hands of the town marshall (who is several levels higher than the PCs and can comfortably kick the crap out of them).
3.) If the PCs are nice, people tend to have good memories of previous "nice" adventuring parties and will be helpful.
The PCs tend to get the message really quickly... be an @$$ and everyone is an @$$ back to you. And since there are so many of them - and most of them have things you want/need (like healing, food, magic, etc.) you darn well better not be an @$$.
Then again, maybe I'm just hypersensitive to boorish PCs. The PCs should be the heroes of the story, not the villains.
I had one group that tried to go way out of control. So I had the local town wizard, whom they knew was exceedingly powerful, TPK them when they ran amok in town. He took great pains to make them look as impotent and pathetic as possible before killing them all in cold, unemotional, methodical fashion. When they started whining, I basically said, "look, if you're going to act like @$$holes, pretty soon everyone notices and stops liking you. You're just pissed because everyone is treating you just like you've been treating them. The Golden Rule applies here." They got the message.
--The Sigil
