If you feel that a job is suspicious, you can always flag it for our review by clicking on the "Flag as inappropriate" link located at the upper right of the job posting. The team will review it and if any violations of ToS are confirmed, they will take action directly.
In terms of best practices, you'll definitely want to make sure that you have a contract with a client before starting on any work, and also that they have a verified billing method so that the work you do can be covered by Upwork Payment Protection. I'd also recommend you check out this thread for tips on avoiding suspicious jobs and scams. Hope that helps!