If you’d like to sell some horses, you’d sell to another player. Want to buy some shiny new tools? You’d buy from another player. Almost all the events are completely player created.

Location also comes into play, since you generally end up living next to other people and it’s not a good idea to piss off your neighbors, just as in RL.

People are also happy to help in general. If you’re an established player, you have enough stuff that you don’t mind sharing some of it. It’s common for new players to be gifted some crops when they first settle in an area. Sometimes they’ll even get better tools, horses that the veteran didn’t need, and general help with things that the newbie might not be able to do yet.

There are always some bad apples in the bunch but if you start doing things that people don’t like, they’ll tell their friends who will in turn tell more people…and soon you won’t be able to find anyone who wants you in their village or is willing to buy your goods. A troll would have a pretty lonely life in Wurm.