No it's not, and you still have a burden of a proof on your shoulders. It probably is, indeed, kept up by some degree of anti-competitive practices but it's still not a monopoly but a member of what you call oligopoly, providing a lot of cheap stuff in every of its areas of competition.
I'd like to point out as well that sanctions (not necessarily well-deserved) against Amazon will just destroy some workplaces, mostly lower-qualified ones, which will cause quite a bit of a problem.
I'd like to point out as well that sanctions (not necessarily well-deserved) against Amazon will just destroy some workplaces, mostly lower-qualified ones, which will cause quite a bit of a problem.