Handling civilians

[MThurston]

I have been in too many one shots and I have to listen to PC disrespect shop owners and peasants.

How are DMs handling this type of situations?

Do you have levels or classes for every day people?

Are their guards or mercenaries that work the market?

Too many times I see DMs let this activity go. For me I would say "Move along, I'm not selling to you."

[JackPhoenix]

Commoners are commoners.
Markets generally have guards, even if they are there just to catch thieves.
If you don't know how to behave, you may find the there's an unscheduled price increase for certain customers, or that the shop is temporarily closed.

[Unoriginal]

There is plenty of NPCs statblocks.

Most will be Commoners, but nothing stop a shopkeeper to use the Bandit, Veteran, or Assassin statblocks, or any other statblock for that matter. Old Natt the weapon merchant might have been seargent of the guard, or trained in a Monk dojo in his early years, or maybe he's a Rakshasa in disguise. But most will just be Commoners.

As for guards and the like, most mercantile areas will have security to avoid smart donkey who think they can take rather than pay. In civilised areas the local cops would do that, helped by personal security for the merchants who have the means and the inclination to hire it. This is increased when the goods are very valuables.

That being said, it's true that the shopkeeps can just refuse to do business with those who don't respect them, or increase the prices.

[Max_Killjoy]

Plus commotions are audible, word spreads, and maybe shopkeepers nearby just "go to lunch" when they see the PCs coming.

Even if it's a one-shot, there are consequences to adventures and mercenaries acting like "murder hobos". Hammer those consequences home.