Hi Peter,
While we can't exactly tell you whether a client is trustworthy, there are some general guidelines you should keep in mind when interacting with clients on the platform.
In general, communicating outside of Upwork before a contract starts is a violation of the Terms of Service. A client suggesting taking communication outside of Upwork before a contract begins is a typical red flag for possible scams. If you engage in this, you may open yourself up to scams or fraud and lose Upwork Payment Protection.
A real client will never ask you to give them money to start working, cash a check for them, work for free, or provide your personal information. Whenever you encounter these situations, please report them using the available flagging options so the team can investigate further. Please take some time to read through this article for more information on how you can stay safe on Upwork.
~ Luiggi