I, a graduate student, have started tutoring undergraduates in computer science at my university to help make ends meet. One student who inquired about my services turned me down upon hearing my rates and remarked (in writing) that they might as well just buy solutions to their projects on a particular freelancing website for that price, as their friends do.
Should I tell the professor about this student, in case he wants to review their submissions more closely? I don't have any proof that they have already cheated, but this constitutes strong evidence that they are likely to. In this question, the OP appears to have evidence to suggest that cheating has taken place already, which seems more clear-cut.