I am staying in the Czech Republic on the basis of visa-free travel (Ukraine/Georgia/Moldova…), and I have found a job here. The employer claims that I can start working for him, and he wants money from me to get me a work visa. Should I trust him?
You are not allowed to work during a visa-free stay – you need a work permit and the appropriate type of residence permit. An application for such a permit should be made at the embassy in your country of origin. It is not possible to apply for such a permit in the Czech Republic if you do not have a long-term residence permit in the Czech Republic.