Summary
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This paper provides a systematic survey of existing data marketplaces and data
products therein. Specifically, the authors scraped information about 215,075
data products from 15 data marketplaces. This information included metadata
such as price, description, data category, geographic scope, time range, etc.
Some of the findings obtained from analyzing these products include:
* perhaps surprisingly, most data products are offered for free, with only
  11,823 paid products.
* the paid products are sold mostly under either a subscription-based model
  (for “live” data) or a one-off model.
* the range of data prices is very wide, but prices can often be well predicted
  by simple regression model using features such as number of data points,
  coverage and granularity.
* the relative predictability of prices can be used to build a data quotation
  tool that takes as input the description of a new data product and outputs
  a price quotation.

Comments
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This works provides a valuable empirical study of existing data marketplaces.
The paper is well-written and the methodology is well-documented. The analysis
of the scraped data products is a convincing first step in trying to make sense
of the wide range of data products and the factors driving their prices.

Minor comments:
* the second sentence of the first paragraph in section 6.1 seems to be the
  result of an incomplete editing process and should be rewritten. Probably,
  "We found that...".
* the y-axis in Figure 4 should be labeled “Number of products”.

Conclusion
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I believe that this works is a valuable reference point and asset to the Data
Economy research community and I recommend acceptance.