Service workers who are payed a wage by a capitalist are proletarian. Service work is productive labor. The capitalist is extracting value from their labor.

Whether a barista is proletarian is entirely situational. Some baristas are proletarian. If a barista works for starbucks for example, then they are proletarian. If a barista works for themself and owns the coffee shop, then they are artisan, small business owner, petite bourgeoisie, middle class, etc. Baristas do not inherently fall into a specific economic class. If you ask, "Is a barista working class?", if they work for a capitalist, then yes, if they work for themselves, then no. The discussion is pointless because it could be either. Some baristas are working class, some baristas are not working class.

Cops are not service workers. Being a cop is not a service. Cops do not produce any service or commodity. Cops are never working class.