I have no idea how accurate this info on FindLaw.com is, but according to it, you don't need a lawyer in small claims court (in the US). And according to https://en.wikipedia.org/wiki/Small_claims_court there are many other countries with similar small claim courts: "Australia, Brazil, Canada, England and Wales, Hong Kong, Ireland, Israel, Greece, New Zealand, Philippines, Scotland, Singapore, South Africa, Nigeria and the United States". I know the list of countries is not even close to covering a large amount of Steam users, but I suspect that us Europeans are covered in other ways, so there's that.

The Wikipedia page also mentions the lawyer thing, by the way:

A usual guiding principle in these courts is that individuals ought to be able to conduct their own cases and represent themselves without a lawyer. Rules are relaxed but still apply to some degree. In some jurisdictions, corporations must still be represented by a lawyer in small-claims court.

And I don't think you need to sue Valve in the US. I think they're required to have legal representation in the countries in which they operate, which should enable you to sue them "locally" in many cases. Again, not an expert, so I'm making quite a few assumptions here.