Is it possible to view another user's purchases on Steam?
Solution 1:
When you are looking at a player's profile, there is a section called "Gameplay Stats". At the bottom of this section you will see a link to "View all N games". After that, just click on "All Games" to see all the games they have acquired.
Solution 2:
You can use Steamcalculator, but it requires the user's profile to be public.