Proz.com is a website founded by Henry Dotterer of Syracuse, New York, USA. The domain is registered like a *** site via "GoDaddy" privacy domain registration and it does not list a physical US office address but only a US PO Box.
For a "mebership fee" of 144 USD the registered freelancers receive access to job postings mainly made by translation agencies. There is also a "Certified PRO network" for paying members. However, as proz is only a website but neither an organisation, institution, association, nor registered company, proz cannot "certify" anybody legally, especially not "based on EN 15038" as they promise. The European Norm 15038 for translation services has been developed and exclusively certified by official DIN certification bodies such as DIN CERTO, TÃœV and other national certification bodies of the European Union member states. However, EN 15038 cannot be certified by organisations outside the EU and thus especially not by unregistered businesses such as proz.com. Therefore the offer to receive a "ProZ.com Certified PRO" title and seal is in fact based on the misleading statement that the proz community could anonymously decide about certification "based on EN 15038" although nobody at proz.com holds the official authorisation to certify anybody "based on EN 15038". Finally this is not the only issue with proz.com.
The "excerpt from the EN 15038 standard for quality in the translation industry" on proz.com is a copyright infringement as proz.com does not hold the reproduction rights for the English translation of DIN EN 15038, which is a copyright of Beuth Verlag GmbH.
What is more, proz.com advertises that paying members would benefit form "new client risk management" through the so-called "Blue Board" where members would be able to post non-payment issues with outsourcing agencies. However, each time a freelancer attempts to post a non-payment report or low rating, the moderators step in and make the rating invisible and so help the non-payers and other unreliable outsourcing agencies to get away with their non-payment scam. Moreover, through the moderated censorship of non-payment reports by providers, real scammers have the best ratings on the "Blue Board" and proz.com is helping them to lure more freelancers into the trap. The freelancers are wasting their time making their own experience with bad payers because proz.com is paid more by their agency customers than by their members.
Summary: proz.com is a trap for freelancers and it is a waste of time and money to buy a membership and apply to job postings. At the end of the day, the promises they made about certification and risk management turned out to be misleading statements and empty scams in support of illegal activities. Therefore, proz.com cannot be "the leading source of translation jobs and translation work for freelancers".
Recommended further readings:
1. The ProZ Perversion | No Peanuts! for Translators
2. Il Segno di Caino - The Translator's Hall of Shame: ProZ.com
3. Interview with Henry Dotterer, founder and president of proz.com
4. DIN EN 15038
Review about: Translation Job Board.