You can and you should contribute - Open Street Map
Today I found out that it's actually a lot easier to contribute to Open Street Map than I thought. There are some serious gaps in house addresses in my area and I was painstakingly using the built in browser editor in the browser.
But, you can use a FOSS app (available on fdroid) called StreetComplete that makes it a lot easier to help out filling in the gaps in your local map data.
It's really fun - kind of like Pokémon Go but you are actually making an impact 😁
Even more than on Wikipedia. The problem with Wikipedia is it tries to use a wiki to write about contentious issues like politics, culture war, religion, national conflicts etc. too and wikis just aren't a very suitable mechanism for that. OSM tries to limit itself to completely objective facts about the world, wikis are very well suited for that.
It is a wiki. While anyone can add fake data, there are monitoring tools to make sure that if someone does that, others will notice and remove it again.
Yes and no. If I remember correctly, it was pokemon go utilizing OSM for the kind of Pokemon you could find in a given area which led to some manipulation. You could probably also get away with changing or hiding something in Nowhere, Idaho.
The bigger issue is probably outdated data. Shops or restaurants in urban areas change fairly quickly, it's quite hard to keep up with those.