Recently I received this question: What are the best online resources to acquire data from?

The top sites for data scrape are data aggregators. Why are they top in data extraction?
They are top because they provide the fullest, most comprehensive data [sets]. The data in them are highly categorized. Therefore you do not need to crawl and fetch other resources and then combine multiple-resource data.

Those sites fall into 2 categories:

1. Goods and services aggregators. Eg. AliExpress, Amazon, Craiglist.
2. Personal data and companies data aggregators. Eg. Linkedin, Xing, YellowPages. For such aggregators another name is business directories.

The first category of sites and services is quite wide-spread. These sites and services promote their goods with the goal of being well-known online, to have as many backlinks as possible to them.

The second category, the business directories, does not tend to reveal its data to the public. These directories rather promote their brand and give scraping bots minimum opportunity for data acquiring*.

Consider the following picture where a company’s data aggregator gives to the user only 2 input fields: what and where.

what_where_data_aggregator
You can find more of how to scrape data aggregators in this post.

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*You have to adhere to the ToS of each particular website/web service when you perform its data scraping.