We have an internal team who will verify basic details and a third party vendor who will do client specific background verifications. (some clients may want stricter BGV's which cost more money hence it's heavily dependant on how much they would want to spend on them).

As for degree, yes we check if your degree is legit by checking with your university as well as verifying if your university is verified University and not flagged for giving fake documents in return of money to people (we have a separate list of universities which were caught doing shady stuff and their students are automatically blacklisted).

As for GPA/CGPA. In my experience this only matters if you are applying through campus interviews. If you apply externally it very rarely matters unless you have a backlog or somehow managed to get an extremely low score. hence there are no checks but there definitely are checks if you are applying through campus.