So if I walk into a store, ask the salesperson for a good (under the tacit assumption that I'll pay for it), then walk away without paying, I committed theft of said good. However if an employer asks me for my time and effort (under the written assumption that I will be given a salary), then they walk out on me without paying... they didn't commit a theft of my time and effort?

When does a cash tip become the possession of the server or counter worker in a restaurant? When it is handed to the server at a table; when it is placed in a jar on the counter; or only after the end of the shift, where the ownership has the right to hold or count it first? The story of a restaurant owner scraping tip money comes up regularly in "the court of public opinion" but is it a criminal dispossession?

eones possession with the intent to not return it. The other scenario lacks the element of removal of possession. The employer has not taken money from the employee; rather, he has declined to provide something promised.