Online panels have become an important resource for research in political science, but the financial compensation involved incentivizes respondents to become survey professionals, which raises concerns about data quality. We provide evidence on survey professionalism using behavioral web browsing data from three U.S. samples, recruited via Lucid, YouGov, and Facebook (total n = 3,886). Survey professionalism is common but varies across samples: By our most conservative measure, we identify 1.7 percentof respondents on Facebook, 7.9 percent of respondents on YouGov, and 34.3 percentof respondents on Lucid as survey professionals. However, evidence that professionals lower data quality is limited: they do not systematically differ demographically or politically from non-professionals and do not respond more randomly—although they are somewhat more likely to speed, to straightline, and to take questionnaires repeatedly. While concerns are warranted, we conclude that survey professionals do not, by and large, distort inferences of research based on online panels.