Inga -

That is the correct way to think about it: "Does one category of respondent likely have a higher response rate than another?" 

In weighting (or reweighting) "response propensity" groups found for nonresponse, one notes categories for which response rates may differ. 

You could try categorizing your respondents by whatever various criteria you can imagine, and check those response rates.   You might then see if the lower response rate groups might be thought to involve satisfaction in some way. 

You have to have the number of possible respondents, and number in each category, to check your response rates. 

Category/group could be anything you think may be important, such as those who previously took a related course, indicating an aptitude and/or interest in the topic/subject matter.  In that case, those who did have previous experience may not tend to have a particular level of satisfaction, but if their response rate is higher, then their responses may be more meaningful.  You have to consider different possible meanings for results which have multiple influencing factors. 

Best wishes - Jim

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PS -

There may be something of interest to you in papers by Mike Brick, such as these:

J. Michael Brick on Inference from Nonprobability Sampling:

............... 

This may be of interest:

"2014 WSS PRESIDENT’S INVITED SEMINAR,"

 http://washstat.org/seminars/2014/20140326_brick.html

In that seminar, Mike Brick addressed a committee report on non-probability sampling of many types:

https://www.researchgate.net/publication/273561892_Summary_Report_of_the_AAPOR_Task_Force_on_Non-probability_Sampling

...............

 "The Future of Survey Sampling"

 Article in Public Opinion Quarterly 75(5):872-888 · December 2011

Impact Factor: 2.25 · DOI: 10.2307/41345915

 https://www.researchgate.net/publication/261967521_The_Future_of_Survey_Sampling

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"Beyond traditional survey taking: adapting to a changing world

Explorations in Non-Probability Sampling Using the Web," J. Michael Brick 

Proceedings of Statistics Canada Symposium 2014

http://www.statcan.gc.ca/sites/default/files/media/14252-eng.pdf

Article The Future of Survey Sampling

Article Summary Report of the AAPOR Task Force on Non-probability Sampling

SCHOLZ, S. (2006) Online-Befragungen an der Universität: Teilnahmebereitschaft, Nonresponse und Adresspoolbeitritt am Beispiel Bremer Studierender; auf emphas.uni-bremen.de.

A very enlightening study with interesting ideas and concepts.

Nulty, D. D. (2008). The adequacy of response rates to online and paper surveys: what can be done?. Assessment & evaluation in higher education, 33(3), 301-314.

I agree with Jens Hepper.

Good Abdullah Noori .