Online panel for survey - can it be representative?

H

I am thinking of using a company that has an online panel to recruit participants for a questionnaire study. Because the demographics (age, gender, region etc) of the entire population is known, they say that they can claim representativeness of the results as they can ensure the demographics of the sample matches the population. Does this sound right? (sample would be at 95% confidence levels with 5% confidence interval).

36924