From the Business Insider excerpting policy:
We excerpt others the way we hope others will excerpt us.
What does that mean? It means that if you think our stuff is worth bringing to your readers’ attention, we are honored and grateful. Please excerpt it as liberally as you want. In return, please just give us clear credit, links back, and an incentive for interested readers to visit our site. (Not all readers–some.)
This is an issue I agonise over a fair bit, and it’s interesting to learn that BI are actually somewhat more permissive in this area than I would expect them to be.
To be clear: As long as you give us credit and links, we are not particularly concerned with the length of the excerpt. Frankly, we’d rather have your readers read our words than your summary of our words, and we see no reason why you should waste your time re-writing something that we’ve already tried to say clearly. (If we’ve garbled it, by all means…) If you occasionally feel you need to run our whole post to make the point, go ahead and run it. Just consider adding a “Related” link to another of our stories so some of your readers might come and check us out.
Our Excerpting Policy – businessinsider.com
I have discovered that there is something of an art to picking an excerpt. I like to choose a small paragraph that encapsulates the key point of an article. Often it’s the second or third paragraph, as the writer will use the opening to cover some background. Otherwise it’s usually one of the closing paragraphs where the writer summarises their point. In longer articles, the key insight could be in the middle somewhere. Wherever the excerpt comes from, I’ll usually have to write a sentence to contextualise.
In my view, large excerpts should be unnecessary in most cases. If you’re just posting interesting links (as I try to do) then the whole idea is to send readers to the source. My job with link posts is to tell people as quickly as possible why something is worth reading, and to clearly signpost the link to the source.