You make that determination. However, we can't give legal advice so you may want to consult an attorney. That said, Fair Use (a USA legal term, there are similar in other countries) is generally a "reasonable" amount of text...but there is no (again a generalization) fixed number of "words" or "paragraphs" specified to determine Fair Use.
Scraping, however is just that and a DMCA (USA specific, also honored in some other countries) is appropriate. Else find the correct filing to be made in other countries. In any event, file a DMCA with the search engines (B, G and Y, etc.) regarding the offending website.
Again, this is only opinion, not legal advice!
(Me? I give 'em a sentence... more than that I land on 'em like a ton of bricks!)
I would search for the Fair Use page at Stanford University.. It is an excellent resource on this issue.
There is no "Magic" word count and it can be as little as no words at all to as much as the full work depending on many factors.
I can tell you that who I work for is pretty generous when it comes to allowable use, but they excercise DMCA with your host and the SE's as well as litigation very successfully when someone violates the company's copyright.
You don't need to break out a tape measure on this sort of thing. It is unlikely to be considered fair use if they pass it off as their own content, not giving you credit. A couple a paragraphs of identical text makes it pretty clear that they copied it.
Just DMCA notify amazon that it is copied from you. I'll bet they take it down.